Systems and methods for backwards-compatible preamble formats for multiple access wireless communication

ABSTRACT

Systems, methods, and devices for wireless communication are disclosed herein. One aspect of the disclosure provides a method of transmitting on a wireless communication network. The method includes transmitting to one or more first devices in a first portion of a bandwidth, the one or more first devices having a first set of capabilities, simultaneously transmitting to one or more second devices in a second portion of the bandwidth, the one or more second devices having a second set of capabilities, and wherein the transmission comprises a preamble which includes an indication for devices with the second set of capabilities to locate a frequency band in the bandwidth for symbols containing a set of transmission parameters for devices with the second set of capabilities, and where the indication is sent so as to have no substantial impact on a preamble decoding of devices with the first set of capabilities.

CLAIM OF PRIORITY UNDER 35 U.S.C. §119

The present application for patent claims priority to ProvisionalApplication No. 61/812,136 entitled “SYSTEMS AND METHODS FORBACKWARDS-COMPATIBLE PREAMBLE FORMATS FOR MULTIPLE ACCESS WIRELESSCOMMUNICATION” filed Apr. 15, 2013, and assigned to the assignee hereofand hereby expressly incorporated by reference herein. The presentapplication for patent further claims priority to ProvisionalApplication No. 61/819,028 entitled “SYSTEMS AND METHODS FORBACKWARDS-COMPATIBLE PREAMBLE FORMATS FOR MULTIPLE ACCESS WIRELESSCOMMUNICATION” filed May 3, 2013, and assigned to the assignee hereofand hereby expressly incorporated by reference herein. The presentapplication for patent further claims priority to ProvisionalApplication No. 61/847,525 entitled “SYSTEMS AND METHODS FORBACKWARDS-COMPATIBLE PREAMBLE FORMATS FOR MULTIPLE ACCESS WIRELESSCOMMUNICATION” filed Jul. 17, 2013, and assigned to the assignee hereofand hereby expressly incorporated by reference herein. The presentapplication for patent further claims priority to ProvisionalApplication No. 61/871,267 entitled “SYSTEMS AND METHODS FORBACKWARDS-COMPATIBLE PREAMBLE FORMATS FOR MULTIPLE ACCESS WIRELESSCOMMUNICATION” filed Aug. 28, 2013, and assigned to the assignee hereofand hereby expressly incorporated by reference herein. The presentapplication for patent further claims priority to ProvisionalApplication No. 61/898,809 entitled “SYSTEMS AND METHODS FORBACKWARDS-COMPATIBLE PREAMBLE FORMATS FOR MULTIPLE ACCESS WIRELESSCOMMUNICATION” filed Nov. 1, 2013, and assigned to the assignee hereofand hereby expressly incorporated by reference herein.

BACKGROUND

1. Field

The present application relates generally to wireless communications,and more specifically to systems, methods, and devices to enablebackward-compatible multiple access wireless communication. Certainaspects herein relate to orthogonal frequency-division multiple access(OFDMA) communications, especially in the IEEE 802.11 family of wirelesscommunication standards.

2. Background

In many telecommunication systems, communications networks are used toexchange messages among several interacting spatially-separated devices.Networks may be classified according to geographic scope, which couldbe, for example, a metropolitan area, a local area, or a personal area.Such networks may be designated respectively as a wide area network(WAN), metropolitan area network (MAN), local area network (LAN), orpersonal area network (PAN). Networks also differ according to theswitching/routing technique used to interconnect the various networknodes and devices (e.g., circuit switching vs. packet switching), thetype of physical media employed for transmission (e.g., wired vs.wireless), and the set of communication protocols used (e.g., Internetprotocol suite, SONET (Synchronous Optical Networking), Ethernet, etc.).

Wireless networks are often preferred when the network elements aremobile and thus have dynamic connectivity needs, or if the networkarchitecture is formed in an ad hoc, rather than fixed, topology.Wireless networks employ intangible physical media in an unguidedpropagation mode using electromagnetic waves in the radio, microwave,infra-red, optical, etc. frequency bands. Wireless networksadvantageously facilitate user mobility and rapid field deployment whencompared to fixed wired networks.

SUMMARY

The systems, methods, and devices of the invention each have severalaspects, no single one of which is solely responsible for its desirableattributes. Without limiting the scope of this invention as expressed bythe claims which follow, some features will now be discussed briefly.After considering this discussion, and particularly after reading thesection entitled “Detailed Description” one will understand how thefeatures of this invention provide advantages that include efficient useof the wireless medium.

One aspect of the disclosure provides a method of transmitting on awireless communication network. The method includes transmitting to oneor more first devices in a first portion of a bandwidth, the one or morefirst devices having a first set of capabilities, simultaneouslytransmitting to one or more second devices in a second portion of thebandwidth, the one or more second devices having a second set ofcapabilities, and wherein the transmission comprises a preamble whichincludes an indication for devices with the second set of capabilitiesto locate a frequency band in the bandwidth for symbols containing a setof transmission parameters for devices with the second set ofcapabilities, and where the indication is sent so as to have nosubstantial impact on a preamble decoding of devices with the first setof capabilities.

The indication may include a code transmitted in the first portion ofthe bandwidth. The code may be carried on an imaginary axis of datatones in one or more signal fields in the preamble. The code may includea one-bit code transmitted in the first portion of the bandwidth. Theindication may include a code transmitted in the second portion of thebandwidth. The first portion of the bandwidth of the packet may includea primary channel and the second portion of the bandwidth may includeone or more secondary channels. The preamble may be transmitted in thefirst portion of the bandwidth, further including transmitting one ormore copies of the preamble in each portion of the bandwidth that willbe used to simultaneously transmit to the one or more second devices, atleast a portion of the one or more copies including the indication.Simultaneously transmitting to one or more second devices in a secondportion of the bandwidth may be simultaneously transmitting a secondpreamble to one or more second devices in a second portion of thebandwidth, the second preamble including the set of transmissionparameters for the one or more second devices having the second set ofcapabilities. The transmission parameters may include an indication ofintended recipients of the transmission in the second portion of thebandwidth.

One aspect of the disclosure provides an apparatus for wirelesscommunication. The apparatus includes a transmitter configured totransmit over a bandwidth, including transmitting to one or more firstdevices in a first portion of a bandwidth, the one or more first deviceshaving a first set of capabilities; simultaneously transmitting to oneor more second devices in a second portion of the bandwidth, the one ormore second devices having a second set of capabilities; and wherein thetransmission includes a preamble which includes an indication fordevices with the second set of capabilities to locate a frequency bandin the bandwidth for symbols containing a set of transmission parametersfor devices with the second set of capabilities, and where theindication is sent so as to have no substantial impact on a preambledecoding of devices with the first set of capabilities.

The indication may include a code transmitted in the first portion ofthe bandwidth. The first portion of the bandwidth of the packet mayinclude a primary channel and wherein the second portion of thebandwidth of the packet may include one or more secondary channels. Thepreamble may be transmitted in the first portion of the bandwidth, andthe transmitted may be further configured to transmit one or more copiesof the preamble in each portion of the bandwidth that will be used tosimultaneously transmit to the one or more second devices, at least aportion of the one or more copies including the indication.Simultaneously transmitting to one or more second devices in a secondportion of the bandwidth may include simultaneously transmitting asecond preamble to one or more second devices in a second portion of thebandwidth, the second preamble including the set of transmissionparameters for the one or more second devices having the second set ofcapabilities.

One aspect of the present disclosure includes a method of receiving on awireless communication network. The method includes receiving a preamblein a first portion of a bandwidth, the preamble transmitted in a formatcompatible with devices having a first set of capabilities; determiningwhether the preamble contains information sufficient to inform deviceshaving a second set of capabilities to locate a signal field in a secondportion of the bandwidth, wherein the first portion and the secondportion of the bandwidth are non-overlapping; and receiving the signalfield in the second portion of the bandwidth.

The method may further include receiving data in the second portion ofthe bandwidth. The first portion of the bandwidth may include a primarychannel, and wherein the second portion of the bandwidth may include oneor more secondary channels. The information may include a one-bit codetransmitted in the preamble. The one-bit code may be carried on animaginary axis of data tones in one or more signal fields in thepreamble. The information in the preamble may have no substantial impacton a preamble decoding of devices with the first set of capabilities.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a channel allocation for channels available for IEEE802.11 systems.

FIG. 2 illustrates a structure of a physical-layer packet (PPDU frame)which may be used in an IEEE 802.11a/b/g/j/p communication.

FIG. 3 illustrates a structure of a physical-layer packet (PPDU frame)which may be used in an IEEE 802.11n communication.

FIG. 4 illustrates a structure of a physical-layer packet (PPDU frame)which may be used in an IEEE 802.11ac communication.

FIG. 5 illustrates an exemplary structure of a downlink physical-layerpacket which may be used to enable backward-compatible multiple accesswireless communications.

FIG. 6 illustrates an exemplary illustration of a signal which may beused to identify STAs and to allocate sub-bands to those STAs.

FIG. 7 illustrates a 2^(nd) exemplary structure of a downlinkphysical-layer packet which may be used to enable backward-compatiblemultiple access wireless communications.

FIG. 8 illustrates a 3^(rd) exemplary structure of a downlinkphysical-layer packet which may be used to enable backward-compatiblemultiple access wireless communications.

FIG. 9 illustrates a 4^(th) exemplary structure of a downlinkphysical-layer packet which may be used to enable backward-compatiblemultiple access wireless communications.

FIG. 10 illustrates an example of a wireless communication system inwhich aspects of the present disclosure may be employed.

FIG. 11 shows a functional block diagram of an exemplary wireless devicethat may be employed within the wireless communication system of FIG. 1.

FIG. 12 illustrates an exemplary structure of an uplink physical-layerpacket which may be used to enable backward-compatible multiple accesswireless communications.

FIG. 13 illustrates a process flow diagram for an example method of atransmitting a high-efficiency packet to two or more wirelesscommunication devices.

FIG. 14 illustrates an exemplary structure of a hybrid downlinkphysical-layer packet which may be used to enable backward-compatiblemultiple access wireless communications.

FIG. 15 illustrates an exemplary method of transmitting a hybrid packet.

FIG. 16 illustrates an exemplary method of receiving a hybrid packet.

FIG. 17 illustrates a packet with one example HE preamble format.

FIG. 18 illustrates a packet with another example HE preamble format.

FIG. 19 illustrates a packet with another example HE preamble format.

FIG. 20 illustrates example bit allocation for an HE-SIG 1 field.

FIG. 21 illustrates an exemplary structure of an uplink physical-layerpacket which may be used to enable backward-compatible multiple accesswireless communications.

FIG. 22 illustrates another exemplary structure of an uplinkphysical-layer packet which may be used to enable backward-compatiblemultiple access wireless communications.

FIG. 23 illustrates an exemplary method of receiving a packet.

FIG. 24 is an exemplary uplink packet structure for an uplink HE packet.

FIG. 25 is exemplary uplink packet structure for an uplink HE packet.

FIG. 26 is an exemplary downlink message from the AP which includesinformation on how many spatial streams each transmitting device mayuse.

FIG. 27 is an illustration of a tone-interleaved LTF which may be usedin an UL OFDMA packet.

FIG. 28 is an illustration of a sub-band interleaved LTF which may beused in an UL OFDMA packet.

FIG. 29 is an exemplary LTF portion of a packet which may be transmittedin an UL OFDMA packet.

FIG. 30 is an illustration of a packet with a common SIG field prior tothe HE-STF and per-user SIG field after all of the HE-LTFs.

FIG. 31 illustrates an exemplary method of transmitting to one or moredevices in a single transmission.

FIG. 32 illustrates an exemplary method of transmitting to one or morefirst devices with a first set of capabilities and simultaneouslytransmitting to one or more second devices with a second set ofcapabilities.

FIG. 33 illustrates an exemplary method of receiving a transmissioncompatible with both devices with a first set of capabilities anddevices with a second set of capabilities.

FIG. 34 illustrates an exemplary method of receiving a transmission,where portions of the transmission are transmitted by different wirelessdevices.

FIG. 35 illustrates various components that may be utilized in awireless device that may be employed within the wireless communicationsystem.

DETAILED DESCRIPTION

Various aspects of the novel systems, apparatuses, and methods aredescribed more fully hereinafter with reference to the accompanyingdrawings. The teachings disclosed may, however, be embodied in manydifferent forms and should not be construed as limited to any specificstructure or function presented throughout this disclosure. Rather,these aspects are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the disclosure to thoseskilled in the art. Based on the teachings herein one skilled in the artshould appreciate that the scope of the disclosure is intended to coverany aspect of the novel systems, apparatuses, and methods disclosedherein, whether implemented independently of or combined with any otheraspect of the invention. For example, an apparatus may be implemented ora method may be practiced using any number of the aspects set forthherein. In addition, the scope of the invention is intended to coversuch an apparatus or method which is practiced using other structure,functionality, or structure and functionality in addition to or otherthan the various aspects of the invention set forth herein. It should beunderstood that any aspect disclosed herein may be embodied by one ormore elements of a claim.

Although particular aspects are described herein, many variations andpermutations of these aspects fall within the scope of the disclosure.Although some benefits and advantages of the preferred aspects arementioned, the scope of the disclosure is not intended to be limited toparticular benefits, uses, or objectives. Rather, aspects of thedisclosure are intended to be broadly applicable to different wirelesstechnologies, system configurations, networks, and transmissionprotocols, some of which are illustrated by way of example in thefigures and in the following description of the preferred aspects. Thedetailed description and drawings are merely illustrative of thedisclosure rather than limiting, the scope of the disclosure beingdefined by the appended claims and equivalents thereof.

Wireless network technologies may include various types of wirelesslocal area networks (WLANs). A WLAN may be used to interconnect nearbydevices together, employing widely used networking protocols. Thevarious aspects described herein may apply to any communicationstandard, such as WiFi or, more generally, any member of the IEEE 802.11family of wireless protocols. For example, the various aspects describedherein may be used as part of a IEEE 802.11 protocol, such as an 802.11protocol which supports orthogonal frequency-division multiple access(OFDMA) communications.

It may be beneficial to allow multiple devices, such as STAs, tocommunicate with an AP at the same time. For example, this may allowmultiple STAs to receive a response from the AP in less time, and to beable to transmit and receive data from the AP with less delay. This mayalso allow an AP to communicate with a larger number of devices overall,and may also make bandwidth usage more efficient. By using multipleaccess communications, the AP may be able to multiplex OFDM symbols to,for example, four devices at once over an 80 MHz bandwidth, where eachdevice utilizes 20 MHz bandwidth. Thus, multiple access may bebeneficial in some aspects, as it may allow the AP to make moreefficient use of the spectrum available to it.

It has been proposed to implement such multiple access protocols in anOFDM system such as the 802.11 family by assigning different subcarriers(or tones) of symbols transmitted between the AP and the STAs todifferent STAs. In this way, an AP could communicate with multiple STA'swith a single transmitted OFDM symbol, where different tones of thesymbol were decoded and processed by different STA's, thus allowingsimultaneous data transfer to multiple STA's. These systems aresometimes referred to as OFDMA systems.

Such a tone allocation scheme is referred to herein as a“high-efficiency” (HE) system, and data packets transmitted in such amultiple tone allocation system may referred to as high-efficiency (HE)packets. Various structures of such packets, including backwardcompatible preamble fields are described in detail below.

Various aspects of the novel systems, apparatuses, and methods aredescribed more fully hereinafter with reference to the accompanyingdrawings. This disclosure may, however, be embodied in many differentforms and should not be construed as limited to any specific structureor function presented throughout this disclosure. Rather, these aspectsare provided so that this disclosure will be thorough and complete, andwill fully convey the scope of the disclosure to those skilled in theart. Based on the teachings herein one skilled in the art shouldappreciate that the scope of the disclosure is intended to cover anyaspect of the novel systems, apparatuses, and methods disclosed herein,whether implemented independently of, or combined with, any other aspectof the invention. For example, an apparatus may be implemented or amethod may be practiced using any number of the aspects set forthherein. In addition, the scope of the invention is intended to coversuch an apparatus or method which is practiced using other structure,functionality, or structure and functionality in addition to or otherthan the various aspects of the invention set forth herein. It should beunderstood that any aspect disclosed herein may be embodied by one ormore elements of a claim.

Although particular aspects are described herein, many variations andpermutations of these aspects fall within the scope of the disclosure.Although some benefits and advantages of the preferred aspects arementioned, the scope of the disclosure is not intended to be limited toparticular benefits, uses, or objectives. Rather, aspects of thedisclosure are intended to be broadly applicable to different wirelesstechnologies, system configurations, networks, and transmissionprotocols, some of which are illustrated by way of example in thefigures and in the following description of the preferred aspects. Thedetailed description and drawings are merely illustrative of thedisclosure rather than limiting, the scope of the disclosure beingdefined by the appended claims and equivalents thereof.

Popular wireless network technologies may include various types ofwireless local area networks (WLANs). A WLAN may be used to interconnectnearby devices together, employing widely used networking protocols. Thevarious aspects described herein may apply to any communicationstandard, such as a wireless protocol.

In some aspects, wireless signals may be transmitted according to an802.11 protocol. In some implementations, a WLAN includes variousdevices which are the components that access the wireless network. Forexample, there may be two types of devices: access points (APs) andclients (also referred to as stations, or STAs). In general, an AP mayserve as a hub or base station for the WLAN and an STA serves as a userof the WLAN. For example, an STA may be a laptop computer, a personaldigital assistant (PDA), a mobile phone, etc. In an example, an STAconnects to an AP via a WiFi compliant wireless link to obtain generalconnectivity to the Internet or to other wide area networks. In someimplementations an STA may also be used as an AP.

An access point (AP) may also comprise, be implemented as, or known as abase station, wireless access point, access node or similar terminology.

A station “STA” may also comprise, be implemented as, or known as anaccess terminal (AT), a subscriber station, a subscriber unit, a mobilestation, a remote station, a remote terminal, a user terminal, a useragent, a user device, user equipment, or some other terminology.Accordingly, one or more aspects taught herein may be incorporated intoa phone (e.g., a cellular phone or smartphone), a computer (e.g., alaptop), a portable communication device, a headset, a portablecomputing device (e.g., a personal data assistant), an entertainmentdevice (e.g., a music or video device, or a satellite radio), a gamingdevice or system, a global positioning system device, or any othersuitable device that is configured for network communication via awireless medium.

As discussed above, certain of the devices described herein mayimplement an 802.11 standard, for example. Such devices, whether used asan STA or AP or other device, may be used for smart metering or in asmart grid network. Such devices may provide sensor applications or beused in home automation. The devices may instead or in addition be usedin a healthcare context, for example for personal healthcare. They mayalso be used for surveillance, to enable extended-range Internetconnectivity (e.g., for use with hotspots), or to implementmachine-to-machine communications.

FIG. 1 illustrates a channel allocation for channels available for802.11 systems. Various IEEE 802.11 systems support a number ofdifferent sizes of channels, such as 5, 10, 20, 40, 80, and 160 MHzchannels. For example, and 802.11ac device may support 20, 40, and 80MHz channel bandwidth reception and transmission. A larger channel maycomprise two adjacent smaller channels. For example, an 80 MHz channelmay comprise two adjacent 40 MHz channels. In the currently implementedIEEE 802.11 systems, a 20 MHz channel contains 64 subcarriers, separatedfrom each other by 312.5 kHz. Of these subcarriers, a smaller number maybe used for carrying data. For example, a 20 MHz channel may containtransmitting subcarriers numbered −1 to −28 and 1 to 28, or 56subcarriers. Some of these carriers may also be used to transmit pilotsignals. Over the years, the IEEE 802.11 standard has evolved throughseveral versions. Older versions include the 11a/g and 11n versions. Themost recently released is the 802.11ac version.

FIGS. 2, 3, and 4 illustrates data packet formats for several currentlyexisting IEEE 802.11 standards. Turning first to FIG. 2, a packet formatfor IEEE 802.11a, 11b, and 11g is illustrated. This frame includes ashort training field 22, a long training field 24, and a signal field26. The training fields do not transmit data, but they allowsynchronization between the AP and the receiving STAs for decoding thedata in the data field 28.

The signal field 26 delivers information from the AP to the STA's aboutthe nature of the packet being delivered. In IEEE 802.11a/b/g devices,this signal field has a length of 24 bits, and is transmitted as asingle OFDM symbol at a 6 Mb/s rate using BPSK modulation and a coderate of ½. The information in the SIG field 26 includes 4 bitsdescribing the modulation scheme of the data in the packet (e.g. BPSK,16QAM, 64QAM, etc.), and 12 bits for the packet length. This informationis used by a STA to decode the data in the packet when the packet isintended for the STA. When a packet is not intended for a particularSTA, the STA will defer any communication attempts during the timeperiod defined in the length field of the SIG symbol 26, and may, tosave power, enter a sleep mode during the packet period of up to about5.5 msec.

As features have been added to IEEE 802.11, changes to the format of theSIG fields in data packets were developed to provide additionalinformation to STAs. FIG. 3 shows the packet structure for the IEEE802.11n packet. The 11n addition to the IEEE.802.11 standard added MIMOfunctionality to IEEE.802.11 compatible devices. To provide backwardcompatibility for systems containing both IEEE 802.11a/b/g devices andIEEE 802.11n devices, the data packet for IEEE 802.11n systems alsoincludes the STF, LTF, and SIG fields of these earlier systems, noted asL-STF 22, L-LTF 24, and L-SIG 26 with a prefix L to denote that they are“legacy” fields. To provide the needed information to STA's in an IEEE802.11n environment, two additional signal symbols 140 and 142 wereadded to the IEEE 802.11n data packet. In contrast with the SIG fieldand L-SIG field 26, however, these signal fields used rotated BPSKmodulation (also referred to as QBPSK modulation). When a legacy deviceconfigured to operate with IEEE 802.11a/b/g receives such a packet, itwill receive and decode the L-SIG field 26 as a normal 11a/b/g packet.However, as the device continued decoding additional bits, they will notbe decoded successfully because the format of the data packet after theL-SIG field 26 is different from the format of an 11a/b/g packet, andthe CRC check performed by the device during this process will fail.This causes these legacy devices to stop processing the packet, butstill defer any further operations until a time period has passeddefined by the length field in the initially decoded L-SIG. In contrast,new devices compatible with IEEE 802.11n would sense the rotatedmodulation in the HT-SIG fields, and process the packet as an 802.11npacket. Furthermore, an 11n device can tell that a packet is intendedfor an 11a/b/g device because if it senses any modulation other thanQBPSK in the symbol following the L-SIG 26, it will ignore it as an11a/b/g packet. After the HT-SIG1 and SIG2 symbols, additional trainingfields suitable for MIMO communication are provided, followed by thedata 28.

FIG. 4 illustrates a frame format for the currently existing IEEE802.11ac standard, which added multi-user MIMO functionality to the IEEE802.11 family. Similar to IEEE 802.11n, an 802.11ac frame contains thesame legacy short training field (L-STF) 22 and long training field(L-LTF) 24. An 802.11ac frame also contains a legacy signal field L-SIG26 as described above.

Next, an 802.11ac frame includes a Very High Throughput Signal(VHT-SIG-A1 150 and A2 152) field two symbols in length. This signalfield provides additional configuration information related to 11acfeatures that are not present in 11a/b/g and 11n devices. The first OFDMsymbol 150 of the VHT-SIG-A may be modulated using BPSK, so that any802.11n device listening to the packet will believe the packet to be an802.11a packet, and will defer to the packet for the duration of thepacket length as defined in the length field of the L-SIG 126. Devicesconfigured according to 11a/g will be expecting a service field and MACheader following the L-SIG 26 field. When they attempt to decode this, aCRC failure will occur in a manner similar to the procedure when an 11npacket is received by an 11a/b/g device, and the 11a/b/g devices willalso defer for the period defined in the L-SIG field 26. The secondsymbol 152 of the VHT-SIG-A is modulated with a 90-degree rotated BPSK.This rotated second symbol allows an 802.11ac device to identify thepacket as an 802.11ac packet. The VHT-SIGA1 150 and A2 152 fieldscontain information on a bandwidth mode, modulation and coding scheme(MCS) for the single user case, number of space time streams (NSTS), andother information. The VHT-SIGA1 150 and A2 152 may also contain anumber of reserved bits that are set to “1.” The legacy fields and theVHT-SIGA1 and A2 fields may be duplicated over each 20 MHz of theavailable bandwidth.

After the VHT-SIG-A, an 802.11ac packet may contain a VHT-STF, which isconfigured to improve automatic gain control estimation in amultiple-input and multiple-output (MIMO) transmission. The next 1 to 8fields of an 802.11ac packet may be VHT-LTFs. These may be used forestimating the MIMO channel and then equalizing the received signal. Thenumber of VHT-LTFs sent may be greater than or equal to the number ofspatial streams per user. Finally, the last field in the preamble beforethe data field is the VHT-SIG-B 154. This field is BPSK modulated, andprovides information on the length of the useful data in the packet and,in the case of a multiple user (MU) MIMO packet, provides the MCS. In asingle user (SU) case, this MCS information is instead contained in theVHT-SIGA2. Following the VHT-SIG-B, the data symbols are transmitted.Although 802.11ac introduced a variety of new features to the 802.11family, and included a data packet with preamble design that wasbackward compatible with 11a/g/n devices and also provided informationnecessary for implementing the new features of 11ac, configurationinformation for OFDMA tone allocation for multiple access is notprovided by the 11ac data packet design. New preamble configurations arenecessary to implement such features in any future version of IEEE802.11 or any other wireless network protocol using OFDM subcarriers.Advantageous preamble designs a represented below, especially withreference to FIGS. 3-9.

FIG. 5 illustrates an exemplary structure of a physical-layer packetwhich may be used to enable backward-compatible multiple access wirelesscommunications in this environment.

In this example physical-layer packet, a legacy preamble including L-STF22, L-LTF 26, and L-SIG 26 are included. Each of these may betransmitted using 20 MHz, and multiple copies may be transmitted foreach 20 MHz of spectrum that the AP uses.

This packet also contains an HE-SIG1 symbol 455, an HE-SIG2 symbol 457,and one or more HE-SIG3 symbols 459. The structure of these symbolsshould be backward compatible with IEEE 802.11a/b/g/n/ac devices, andshould also signal OFDMA HE devices that the packet is an HE packet. Tobe backward compatible with IEEE 802.11a/b/g/n/ac devices, appropriatemodulation may be used on each of these symbols. In someimplementations, the first symbol, HE-SIG1 455 may be modulated withBPSK modulation. This will cause the same effect on 11a/b/g/n device asis currently the case with 11ac packets that also have their first SIGsymbol BPSK modulated. For these devices, it does not matter what themodulation is on the subsequent HE-SIG symbols 457, 459. The secondsymbol 457 may be BPSK or QPSK modulated. If BPSK modulated, an 11acdevice will assume the packet is an 11a/b/g packet, and will stopprocessing the packet, and will defer for the time defined by the lengthfield of L-SIG 26. If QBPSK modulated, an 11ac device will produce a CRCerror during preamble processing, and will also stop processing thepacket, and will defer for the time defined by the length field ofL-SIG. To signal HE devices that this is an HE packet, at least thefirst symbol of HE-SIG3 459 may be QBPSK modulated.

The information necessary to establish an OFDMA multiple accesscommunication may be placed in the HE-SIG fields 455, 457, and 459 in avariety of positions. In the example of FIG. 5, HE-SIG1 455 contains thetone allocation information for OFDMA operation. HE-SIG3 459 containsbits defining user specific modulation type for each multiplexed user.In addition, HE-SIG2 457 contains bits defining user specific MIMOspatial streams, such as is provided in the 11ac format of FIG. 4. Theexample of FIG. 5 may allow four different users to be each assigned aspecific sub-band of tones and a specific number of MIMO space timestreams. 12 bits of space time stream information allows three bits foreach of four users such that 1-8 streams can be assigned to each one. 16bits of modulation type data allows four bits for each of four users,allowing assignment of any one of 16 different modulation schemes(16QAM, 64QAM, etc.) to each of four users. 12 bits of tone allocationdata allows specific sub-bands to be assigned to each of four users.

One example SIG field scheme for subband allocation is illustrated inFIG. 6. This example includes a 6 bit Group ID field similar to thatcurrently used in IEEE 802.11ac as well as 10 bits of information toallocate sub-band tones to each of four users. The bandwidth used todeliver the packet 130 may be allocated to STAs in multiples of somenumber of MHz. For example, the bandwidth may be allocated to STAs inmultiples of B MHz. The value of B may be a value such as 1, 2, 5, 10,15, or 20 MHz. The values of B may be provided by the two bit allocationgranularity field of FIG. 6. For example, the HE-SIG 155 may contain onetwo-bit field, which allows for four possible values of B. For example,the values of B may be 5, 10, 15, or 20 MHz, corresponding to values of0-3 in the allocation granularity field. In some aspects, a field of kbits may be used to signal the value of B, defining a number from 0 toN, where 0 represents the least flexible option (largest granularity),and a high value of N represents the most flexible option (smallestgranularity). Each B MHz portion may be referred to as a sub-band.

The HE-SIG1 may further use 2 bits per user to indicate the number ofsub-bands allocated to each STA. This may allow 0-3 sub-bands to beallocated to each user. The group-id (G_ID) concept from 802.11ac may beused in order to identify the STAs which will receive data in an OFDMApacket. This 6-bit G_ID may identify up to four STAs, in a particularorder, in this example.

In this example, the allocation granularity field is set to “00.” Inthis example, the allocation granularity field is a two-bit field, thevalues of which may correspond to 5, 10, 15 or 20 MHz, in order. Forexample, a “00” may correspond to an allocation granularity of 5 MHz.

In this example, the first two bits give the number of sub-bands for thefirst user identified by the G_ID. Here, user-1 is given “11” sub-bands.This may correspond to user-1 receiving 3 sub-bands. If each sub-band is5 MHz, this may mean the user-1 is allocated 15 MHz of spectrum.Similarly, user-2 also receives 3 sub-bands, while user-3 receives zerosub-bands, and user-4 receives 2 sub-bands. Thus, this allocation maycorrespond to a 40 MHz signal, in which 15 MHz is used for both user-1and user-2, while user-4 receives 10 MHz, and user-3 does not receiveany sub-bands.

The training fields and data which is sent after the HE-SIG symbols isdelivered by the AP according to the allocated tones to each STA. Thisinformation may potentially be beamformed. Beamforming this informationmay have certain advantages, such as allowing for more accurate decodingand/or providing more range than non-beamformed transmissions.

Depending on the space time streams assigned to each user, differentusers may require a different number of HE-LTFs 165. Each STA mayrequire a number of HE-LTFs 165 that allows channel estimation for eachspatial stream associated with that STA, which is generally equal to ormore than the number of spatial streams. LTFs may also be used forfrequency offset estimation and time synchronization. Because differentSTA's may receive a different number of HE-LTFs, symbols may betransmitted from the AP that contain HE-LTF information on some tonesand data on other tones.

In some aspects, sending both HE-LTF information and data on the sameOFDM symbol may be problematic. For example, this may increase thepeak-to-average power ratio (PAPR) to too high a level. Thus, it may bebeneficial to instead to transmit HE-LTFs 165 on all tones of thetransmitted symbols until each STA has received at least the requirednumber of HE-LTFs 165. For example, each STA may need to receive oneHE-LTF 165 per spatial stream associated with the STA. Thus, the AP maybe configured to transmit a number of HE-LTFs 165 to each STA equal tothe largest number of spatial streams assigned to any STA. For example,if three STAs are assigned a single spatial stream, but the fourth STAis assigned three spatial streams, in this aspect, the AP may beconfigured to transmit four symbols of HE-LTF information to each of thefour STAs before transmitting symbols containing payload data.

It is not necessary that the tones assigned to any given STA beadjacent. For example, in some implementations, the sub-bands of thedifferent receiving STAs may be interleaved. For example, if each ofuser-1 and user-2 receive three sub-bands, while user-4 receives twosub-bands, these sub-bands may be interleaved across the entire APbandwidth. For example, these sub-bands may be interleaved in an ordersuch as 1,2,4,1,2,4,1,2. In some aspects, other methods of interleavingthe sub-bands may also be used. In some aspects, interleaving thesub-bands may reduce the negative effects of interferences or the effectof poor reception from a particular device on a particular sub-band. Insome aspects, the AP may transmit to STAs on the sub-bands that the STAprefers. For example, certain STAs may have better reception in somesub-bands than in others. The AP may thus transmit to the STAs based atleast in part on which sub-bands the STA may have better reception. Insome aspects, the sub-bands may also not be interleaved. For example,the sub-bands may instead be transmitted as 1,1,1,2,2,2,4,4. In someaspects, it may be pre-defined whether or not the sub-bands areinterleaved.

In the example of FIG. 5, HE-SIG3 symbol modulation is used to signal HEdevices that the packet is an HE packet. Other methods of signaling HEdevices that the packet is an HE packet may also be used. In the exampleof FIG. 7, the L-SIG 126 may contain information that instructs HEdevices that an HE preamble will follow the legacy preamble. Forexample, the L-SIG 26 may contain a low-energy, 1-bit code on the Q-railwhich indicates the presence of a subsequent HE preamble to HE devicessensitive to the Q signal during the L-SIG 26. A very low amplitude Qsignal can be used because the single bit signal can be spread acrossall the tones used by the AP to transmit the packet. This code may beused by high efficiency devices to detect the presence of anHE-preamble/packet. The L-SIG 26 detection sensitivity of legacy devicesneed not be significantly impacted by this low-energy code on theQ-rail. Thus, these devices will be able to read the L-SIG 26, and notnotice the presence of the code, while HE devices will be able to detectthe presence of the code. In this implementation, all of the HE-SIGfields can be BPSK modulated if desired, and any of the techniquesdescribed herein related to legacy compatibility can be used inconjunction with this L-SIG signaling.

FIG. 8 illustrates another method to implement backward compatibilitywith 11ac devices as well. In this example, the HE-SIG-A1 455 maycontain a bit that is set to a value flipped from the value that an 11acdevice requires when decoding a VHT-SIG field. For example, an 802.11acVHT-SIG-A field contains bits 2 and 23 which are reserved and set to 1in a correctly assembled VHT-SIG-A field. In the high efficiencypreamble HE-SIG-A 455, one or both of these bits may be set to zero. Ifan 802.11ac device receives a packet which contains a reserved bit withsuch a flipped value, an 11ac device stop processing the packet,treating it as undecodable, while still deferring to the packet for theduration specified in the L-SIG 26. In this implementation, backwardcompatibility with 11a/b/g/n devices can be achieved by using BPSKmodulation on the HE-SIG1 symbol 455, and signaling HE devices can beachieved by using QBPSK modulation on one or more symbols of HE-SIG2 457or HE-SIG3 459.

As shown by the example illustrated in FIG. 9, the structure of an HEpacket may be based upon the packet structure utilized in 802.11ac. Inthis example, after the legacy preamble 22, 24, 26, two symbols areprovided, termed HE-SIGA1 and HE-SIGA2 in FIG. 9. This is the samestructure as the VHT-SIGA1 and VHT-SIGA2 of FIG. 4. To fit both spacetime stream allocation and tone allocation into these two 24 bitsymbols, less freedom is provided for space time stream options.

The example of FIG. 9 also places an HE-SIGB symbol 459 after the HEtraining fields, which is also analogous to the VHT-SIGB field 154 ofFIG. 4.

However, one potential problem with this 11ac-based preamble is thatthis design may run into space limitations in the HE-SIG-B 470. Forexample, the HE-SIG-B 470 may need to contain at least the MCS (4 bits)and the tail bits (6 bits). Thus, the HE-SIG-B 470 may need to containbe at least 10 bits of information. In the 802.11ac specification, theVHT-SIG-B is one OFDM symbol. However, there may not be a sufficientnumber of bits in a single OFDM symbol, depending upon the bandwidth ofeach sub-band. For example, Table 1 below illustrates this potentialissue.

TABLE 1 BW per user # of bits per # of bits remaining (in MHz) user/OFDMsymbol # of tail bits for MCS field 10 13 6 7 6 8 6 2 5 6 6 0

As illustrated in Table 1, if each sub-band is 10 MHz, a single OFDMsymbol provides 13 bits. Six of these bits are necessary as tail bits,and thus, 7 bits remain for the MCS field. The MCS field, as notedabove, requires four bits. Thus, if each sub-band is at least 10 MHz, asingle OFDM symbol may be used for the HE-SIG-B 470, and this may besufficient to include the 4 bit MCS field. However, if each sub-band isinstead 5 or 6 MHz, this may only allow 6 or 8 bits per OFDM symbol. Ofthese bits, 6 bits are tail bits. Thus, only 0 or 2 bits are availablefor the MCS field. This is insufficient to provide the MCS field. Inthose cases where the sub-band granularity is too small to provide therequired information in the SIGB fields, more than one OFDM symbol maybe used for the HE-SIG-B 470. The number of symbols needed will berelated to the smallest sub-band the system will allow. If this is 5MHz, corresponding to 13 tones in the IEEE 802.11 family OFDM system,two symbols for the HE-SIG-B would allow BPSK modulation and a ½ forwarderror correction code rate to provide 12 bits, which is a sufficientlength for the HE-SIG-B information MCS and tail bits. FIG. 10illustrates an example of a wireless communication system 100 in whichaspects of the present disclosure may be employed. The wirelesscommunication system 100 may operate pursuant to a wireless standard,for example the IEEE 802.11 standards. The wireless communication system100 may include an AP 104, which communicates with STAs 106 a, 106 b,106 c, and 106 d (collectively STAs 106). The network may include bothlegacy STAs 106 b and high efficiency (HE) STAs 106 a, 106 c, 106 d.

A variety of processes and methods may be used for transmissions in thewireless communication system 100 between the AP 104 and the STAs 106.For example, signals may be sent and received between the AP 104 and theSTAs 106 in accordance with OFDM/OFDMA techniques. If this is the case,the wireless communication system 100 may be referred to as anOFDM/OFDMA system.

A communication link that facilitates transmission from the AP 104 toone or more of the STAs 106 may be referred to as a downlink (DL) 108,and a communication link that facilitates transmission from one or moreof the STAs 106 to the AP 104 may be referred to as an uplink (UL) 110.Alternatively, a downlink 108 may be referred to as a forward link or aforward channel, and an uplink 110 may be referred to as a reverse linkor a reverse channel. In some aspects, some DL 108 communications may beHE packets, such as HE packet 130. Such HE packets may contain legacypreamble information, such as preamble information in according withspecifications such as 802.11a and 802.11n, which contains informationsufficient to cause legacy STA 106 b to recognize the HE packet 130 andto defer to the transmission of the HE packet 130 for the duration ofthe transmission. Similarly, the DL 108 communications which are HEpackets 130 may contain information sufficient to inform HE STAs 160 a,106 c, 106 d which devices may receive information in the HE packet 130,as discussed above.

The AP 104 may act as a base station and provide wireless communicationcoverage in a basic service area (BSA) 102. The AP 104 along with theSTAs 106 associated with the AP 104 and that use the AP 104 forcommunication may be referred to as a basic service set (BSS). It shouldbe noted that the wireless communication system 100 may not have acentral AP 104, but rather may function as a peer-to-peer networkbetween the STAs 106. Accordingly, the functions of the AP 104 describedherein may alternatively be performed by one or more of the STAs 106.

FIG. 11 illustrates various components that may be utilized in awireless device 202 that may be employed within the wirelesscommunication system 100. The wireless device 202 is an example of adevice that may be configured to implement the various methods describedherein. For example, the wireless device 202 may comprise the AP 104 orone of the STAs 106 of FIG. 10. In some aspects, the wireless device 202may comprise an AP that is configured to transmit HE packets, such as HEpacket 130.

The wireless device 202 may include a processor 204 which controlsoperation of the wireless device 202. The processor 204 may also bereferred to as a central processing unit (CPU). Memory 206, which mayinclude both read-only memory (ROM) and random access memory (RAM),provides instructions and data to the processor 204. A portion of thememory 206 may also include non-volatile random access memory (NVRAM).The processor 204 typically performs logical and arithmetic operationsbased on program instructions stored within the memory 206. Theinstructions in the memory 206 may be executable to implement themethods described herein. For example if the wireless device 202 is anAP 104, the memory 206 may contain instructions sufficient to allow thewireless device 202 to transmit HE packets, such as HE packet 130. Forexample, the memory 206 may contain instructions sufficient to allow thewireless device 202 to transmit a legacy preamble, followed by an HEpreamble, including an HE-SIG or an HE-SIG-A. In some aspects, thewireless device 202 may include a frame formatting circuit 221, whichmay contain instructions sufficient to allow the wireless device 202 totransmit a frame according to embodiments disclosed herein. For example,the frame formatting circuit 221 may contain instructions sufficient toallow the wireless device 202 to transmit a packet which includes both alegacy preamble and a high-efficiency preamble.

The processor 204 may comprise or be a component of a processing systemimplemented with one or more processors. The one or more processors maybe implemented with any combination of general-purpose microprocessors,microcontrollers, digital signal processors (DSPs), field programmablegate array (FPGAs), programmable logic devices (PLDs), controllers,state machines, gated logic, discrete hardware components, dedicatedhardware finite state machines, or any other suitable entities that canperform calculations or other manipulations of information.

The processing system may also include machine-readable media forstoring software. Software shall be construed broadly to mean any typeof instructions, whether referred to as software, firmware, middleware,microcode, hardware description language, or otherwise. Instructions mayinclude code (e.g., in source code format, binary code format,executable code format, or any other suitable format of code). Theinstructions, when executed by the one or more processors, cause theprocessing system to perform the various functions described herein.

The wireless device 202 may also include a housing 208 that may includea transmitter 210 and a receiver 212 to allow transmission and receptionof data between the wireless device 202 and a remote location. Thetransmitter 210 and receiver 212 may be combined into a transceiver 214.An antenna 216 may be attached to the housing 208 and electricallycoupled to the transceiver 214. The wireless device 202 may also include(not shown) multiple transmitters, multiple receivers, multipletransceivers, and/or multiple antennas.

The wireless device 202 may also include a signal detector 218 that maybe used in an effort to detect and quantify the level of signalsreceived by the transceiver 214. The signal detector 218 may detect suchsignals as total energy, energy per subcarrier per symbol, powerspectral density and other signals. The wireless device 202 may alsoinclude a digital signal processor (DSP) 220 for use in processingsignals. The DSP 220 may be configured to generate a data unit fortransmission. In some aspects, the data unit may comprise a physicallayer data unit (PPDU). In some aspects, the PPDU is referred to as apacket.

The wireless device 202 may further comprise a user interface 222 insome aspects. The user interface 222 may comprise a keypad, amicrophone, a speaker, and/or a display. The user interface 222 mayinclude any element or component that conveys information to a user ofthe wireless device 202 and/or receives input from the user.

The various components of the wireless device 202 may be coupledtogether by a bus system 226. The bus system 226 may include a data bus,for example, as well as a power bus, a control signal bus, and a statussignal bus in addition to the data bus. Those of skill in the art willappreciate the components of the wireless device 202 may be coupledtogether or accept or provide inputs to each other using some othermechanism.

Although a number of separate components are illustrated in FIG. 11, oneor more of the components may be combined or commonly implemented. Forexample, the processor 204 may be used to implement not only thefunctionality described above with respect to the processor 204, butalso to implement the functionality described above with respect to thesignal detector 218 and/or the DSP 220. Further, each of the componentsillustrated in FIG. 11 may be implemented using a plurality of separateelements. Furthermore, the processor 204 may be used to implement any ofthe components, modules, circuits, or the like described below, or eachmay be implemented using a plurality of separate elements.

FIG. 12 illustrates an exemplary structure of an uplink physical-layerpacket 830 which may be used to enable backward-compatible multipleaccess wireless communications. In such an uplink message, no legacypreamble is needed, as the NAV is set by the AP's initial downlinkmessage. Thus, the uplink packet 830 does not contain a legacy preamble.The uplink packet 830 may be sent in response to a UL-OFDMA-announcemessage that is sent by the AP.

The uplink packet 830 may be sent by a number of different STAs. Forexample, each STA that is identified in the downlink packet may transmita portion of the uplink packet 830. Each of the STAs may transmit in itsassigned bandwidth or bandwidths simultaneously, and the transmissionsmay be received by the AP as a single packet.

In the packet 830, each STA uses only the channels, or sub-bands,assigned to it during the tone assignment in the initial downlinkmessage, as discussed above. This allows for completely orthogonalreceive processing on the AP. In order to receive messages on each ofthese sub-bands, the AP must receive pilot tones. These pilot tones areused in 802.11 packets for phase tracking, in order to estimate a phaseoffset per symbol to correct for phase changes across data symbols dueto residual frequency offset or due to phase noise. This phase offsetmay also feed into time and frequency tracking loops.

In order to transmit pilot tones, at least two different options may beused. First, each user may transmit the pilot tones that fall into itsassigned sub-bands. However, for low bandwidth OFDMA allocations, thismay not allow a sufficient number of pilot tones for some users. Forexample, there are 4 pilot tones in a 20 MHz transmission in802.11a/n/ac. However, if a user only has 5 MHz assigned to it, the usermay have only one pilot tone in its sub-band. If some problem, such as adeep fade, occurs with that pilot tone, it may be very difficult toobtain a good phase estimate.

Another possible method of transmitting pilot tones may involve eachuser transmitting on all the pilot tones, not just those which fall inits sub-band. This may result in a larger number of pilot tones beingtransmitted per user. But, this may result in the AP receiving eachpilot tone from multiple users simultaneously, which may be moredifficult for the AP to process. The AP would need to estimate channelsfor all users. In order to accomplish this, more LTFs may be needed,such as one that corresponds to the sum of all users' spatial streams.For example, if each of four users were associated with two spatialstreams, in this approach, eight LTFs may be used.

Thus, each STA may transmit an HE-STF 835. As shown in packet 830, theHE-STF 835 may be transmitted in 8 us, and contain two OFDMA symbols.Each STA may also transmit one or more HE-LTF 840. As shown in packet830, the HE-LTF 840 may be transmitted in 8 us, and contain two OFDMAsymbols. For example, as before, each STA may transmit a HE-LTF 840 foreach sub-band assigned to the STA. Each STA may also transmit a HE-SIG845. The length of the HE-SIG 845 may be one ODFMA symbol long (4 us)for each of U, where U is the number of STAs multiplexed in thetransmission. For example, if four STAs are sending the uplink packet830, the HE-SIG 845 may be 16 us. After the HE-SIG 845, additionalHE-LTFs 840 may be transmitted. Finally, each STA may transmit data 855.

In order to send a combined uplink packet 830, each of the STAs may besynchronized with each other in time, frequency, and in power with theother STAs. The timing synchronization required for such a packet may beon the order of approximately 100 ns. This timing may be coordinated byresponding to the AP's UL-OFDMA-announce message. This timing accuracymay be obtained using several solutions which are known to those ofskill in the art. For example, techniques used by 802.11ac and 802.11ndevices in order to time short interframe space (SIFS) may be sufficientto provide the timing accuracy needed in order to obtain a combineduplink packet 830. This timing accuracy may also be maintained by usingan 800 ns long guard interval only for the uplink OFDMA to get 400 nsguard time, in order to absorb timing errors and round trip delaydifferences between uplink clients.

Another technical issue that must be addressed by the uplink packet 830is that the frequencies of the sending devices must be synchronized.There are multiple options to deal with frequency-offset synchronizationamong STAs in an UL-OFDMA system, such as that of uplink packet 830.First, each STA may calculate and correct for its frequency differences.For example, the STAs may calculate a frequency offset with respect tothe AP, based upon the UL-OFDMA-announce message sent to the STAs. Basedupon this message, the STAs may apply a phase ramp on the time-domainuplink signal. The AP may also estimate the common phase offset for eachSTA, using the LTFs. For example, the LTFs which are transmitted by theSTAs may be orthogonal in frequency. Hence, the AP can use a windowedinverse fast Fourier transform (IFFT) function to separate the STAimpulse responses. The variation of these impulse responses across twoidentical LTF symbols may give us a frequency offset estimate for everyuser. For example, frequency offset in a STA may lead to phase ramp,over time. Thus, if two identical LTF symbols are transmitted, the APmay be able to use the differences between the two symbols to calculatea slope of the phase across the two impulse responses in order to get anestimate of the frequency offset. This approach may be similar to thetone-interleaved approach that has been proposed in UL-MU-MIMO message,which may be known to persons of skill in the art.

FIG. 13 illustrates a process flow diagram for an example method of atransmitting a high-efficiency packet to two or more wirelesscommunication devices. This method may be done by a device, such as anAP.

At block 905, the AP transmits a legacy preamble, the legacy preamblecontaining information sufficient to inform legacy devices to defer tothe packet. For example, the legacy preamble may be used to alert legacydevices to defer to the packet. The legacy packet may contain a reservedbit or a combination of reserved bits. These reserved bits may alerthigh-efficiency devices to continue listening to the packet for ahigh-efficient preamble, while also causing legacy devices to defer tothe packet. In some aspects, the means for transmitting a legacypreamble, the legacy preamble containing information sufficient toinform legacy devices to defer to the packet, may comprise atransmitter.

At block 910, the AP transmits a high-efficiency signal, thehigh-efficiency signal containing tone allocation information, the toneallocation information identifying two or more wireless communicationdevices. In some aspects, the high-efficiency signal may contain toneallocation information, which may include information that identifiesthe STAs that will receive information in the packet, and may alertthose STAs which sub-bands are intended for them. In some aspects, thehigh-efficiency packet may also include information sufficient to cause802.11ac devices to defer to the packet. In some aspects, the means fortransmitting a high-efficiency signal, the high-efficiency signalcontaining tone allocation information, the tone allocation informationidentifying two or more wireless communication devices may comprise atransmitter. In some aspects, the high-efficiency signal may furthercomprise an indication of a number of spatial streams may be assigned toeach of the two or more wireless communications devices. For example,each of the two or more wireless communications devices may be assignedone or more spatial streams. In some aspects, the means for assigningone or more spatial streams to each of the two or more wirelesscommunications devices may comprise a transmitter or a processor.

At block 915, the AP transmits data to the two or more wirelesscommunication devices simultaneously, the data contained on two or moresub-bands. For example, the AP may transmit data to up to four STAs. Insome aspects, the means for transmitting data to the two or morewireless communication devices simultaneously, the data contained on twoor more sub-bands may comprise a transmitter.

In some aspects, an AP may transmit a hybrid packet, which includes datafor both for a legacy device, such as an IEEE 802.11a/n/ac device, anddata for one or more high-efficiency devices. Such a hybrid packet mayallow more efficient uses of bandwidth in mixed environments containingboth legacy and high-efficiency devices. For example, in a legacy systemif an AP is configured to use 80 MHz, a portion of the bandwidthassigned to the AP may go unused if the AP is transmitting a packet to adevice that is not capable of using the full 80 MHz. This is one problemthat is addressed by the use of high-efficiency packets. However, in anenvironment in which some of the STAs are high-efficiency and some ofthe STAs are legacy devices, bandwidth may still go unused whentransmitting to legacy devices that are not capable of using the fullbandwidth that the AP is configured to use. For example, while thehigh-efficiency packets in such a system may use the full bandwidth, asdiscussed above, legacy packets may not. Thus, it may be beneficial toprovide a hybrid packet, in which a legacy device may receiveinformation in one portion of the bandwidth of a packet, whilehigh-efficiency devices may receive information in another portion ofthe packet. Such a packet may be referred to as a hybrid packet, as aportion of the packet may transmit data in a legacy-compatible format,such as IEEE 802.11a/n/ac, and a portion of the packet may transmit datato high-efficiency devices.

An exemplary hybrid packet 1400 is illustrated in FIG. 14. Such a hybridpacket may be transmitted by a wireless device, such as an AP. A hybridpacket may include a legacy portion, in which data is transmitted to alegacy device, and a high-efficiency portion, in which data istransmitted to a high-efficiency device.

A hybrid packet 1400 may include a number of legacy preambles, eachduplicated over some portion of the bandwidth of the packet. Forexample, the exemplary hybrid packet 1400 is illustrated as an 80 MHzpacket, which contains four 20 MHz legacy preambles duplicated over the80 MHz of bandwidth of the packet 1400. Such duplication may be used inlegacy formats, in order to ensure that other devices, which may operateon only a portion of the 80 MHz bandwidth, defer to the packet. In someaspects each of the devices in the network may, by default, monitor onlythe primary channel.

A hybrid packet 1400 may include an L-STF 1405 and an L-LTF 1410 whichare the same as those specified in legacy formats, such as IEEE802.11a/n/ac. These fields may be the same as those discussed above.However, the L-SIG 1415 of a hybrid packet 1400 may differ from that ofa legacy packet. The L-SIG 1415 may contain information which is used tosignal to high-efficiency devices that the packet is a hybrid packet. Inorder for legacy devices to be able to also receive information in thepacket, this information must be hidden from the legacy devices, suchthat it does not disrupt their reception of the L-SIG 1415.

The L-SIG 1415 may signal to high-efficiency devices that the packet isa hybrid packet by placing a one-bit code orthogonal to the informationin the L-SIG 1415. For example, as discussed above, a one-bit code maybe placed on the Q-rail of the L-SIG 1415. Legacy devices may not noticethe one-bit code, and may be able to read the L-SIG 1415 as normal,while high-efficiency devices may look specifically for this one-bitcode, and be able to determine whether or not it is present. Thisone-bit code may be used to signal to high-efficiency devices that ahybrid packet is being sent. In some aspects, the one-bit code may behidden from or invisible to legacy devices, which may not be configuredto look for the code. In some aspects, legacy devices may be able tounderstand the L-SIG 1415 without observing any irregularities due tothe presence of the one-bit code. In some aspects, only the L-SIG 1415in the primary channel may contain the one-bit code to instructhigh-efficiency devices to look at other channels for an HE-SIG 1425. Insome aspects, a number of L-SIGs 1415 may have this one-bit indicator,where the number of L-SIGs 1415 with the indicator is equal to thenumber of channels which are to be used for the legacy packet. Forexample, if the legacy packet will include both the first and secondchannels, but not a third channel, then the L-SIG in the first andsecond channels may contain the one-bit indicator, while the L-SIG inthe third channel may not contain this indicator. High-efficiencydevices may be configured to look for the first channel with an L-SIGthat does not contain a one-bit code, and to monitor that channel forthe presence of an HE-SIG 1425. In some aspects, the bandwidthinformation in a VHT-SIG-A 1420 may contain information regarding howmuch bandwidth the legacy packet 1430 will use, and thus, at whichbandwidth the HE packet 1435 may begin. In some aspects, the one-bitcode may only be included in L-SIGs 1415 which are being transmitted inchannels which will be used for transmitting data to HE devices. Forexample, if the first channel is used to transmit to a legacy device,and three other channels are used to transmit to HE devices in aparticular packet, each of the L-SIGs 1415 transmitted in the threeother channels may include the one-bit code. In some aspects, in an HEpacket, each L-SIG 1415 may include the one-bit code to indicate thateach channel may be used to transmit data to HE devices. In someaspects, this may allow the bandwidth used for the HE portion of an HEpacket or a hybrid packet to be signaled using the L-SIG 1415 of thepacket. If the bandwidth used for the HE portion of the packet issignaled in the L-SIG 1415, this may allow the HE-SIG 1425 in a HEpacket or a hybrid packet to span a larger portion of the bandwidthassigned to the HE portion of the packet. For example, the HE-SIG 1425may be configured to span the bandwidth assigned to the HE packet. Insome aspects, using more bandwidth for the HE-SIG 1425, rather than onlyusing 20 MHz for the HE-SIG 1425, may allow more information to betransmitted in the HE-SIG 1425. In some aspects, the first symbol of theHE-SIG 1425 may be transmitted in duplicate on each 20 MHz of thebandwidth assigned to the HE portion of the packet, while the remainingsymbols of the HE-SIG 1425 may be transmitted using the full bandwidthassigned to the HE portion of the packet. For example, the first symbolof the HE-SIG 1425 may be used to transmit the bandwidth allocated tothe HE portion of the HE or hybrid packet, and thus, subsequent symbolsmay be transmitted on the entire bandwidth assigned to the HE portion ofthe packet.

Upon receiving the one-bit code in the L-SIG 1415, high-efficiencydevices may be configured to look in higher-bandwidth portions of thebandwidth allocated to the AP, such as higher-bandwidth channels, tofind an HE-SIG 1425. For example, in the hybrid packet 1400, uponreceiving the L-SIG 1415 with the one-bit code in an orthogonaldirection, high-efficiency devices may be configured to look in the 20MHz channels apart from the channel carrying data to legacy devices forHE-SIGs, such as HE-SIG 1425, which may be transmitted in otherfrequency bands, alongside a legacy packet. For example, in exemplaryhybrid packet 1400, HE-SIG 1425 is illustrated as being transmittedsimultaneously with VHT-SIG-A 1420. In this example, the hybrid packet1400 may include an IEEE 802.11ac-compatible packet on the lower portionof the bandwidth, and a high-efficiency packet on the higher portion ofthe bandwidth. The hybrid packet 1400 may also contain an IEEE 802.11aor IEEE 802.11n-compatible packet in the lower portion. Importantly,regardless of which type of packet the lower portion is, the L-SIG 1415may be configured to contain signaling information, sufficient to signalto high-efficiency devices that the packet is a hybrid packet, and thus,to look for an HE-SIG 1425 in another frequency.

In some aspects, the HE-SIG 1425 may be similar to any of the previoushigh-efficiency signal fields previously discussed. In some aspects, anAP which transmits both high-efficiency packets and hybrid packets mayuse a symbol with a rotated BPSK constellation (QBPSK) symbol in anHE-SIG 1425 to indicate that a packet is a high-efficiency packet,rather than using a one-bit signal in the Q-rail, as using a one-bitsignal on the Q-rail may instead be used to signal that a packet is ahybrid packet, such as hybrid packet 1400. For example, the HE-SIG 1425may be used to indicate to high-efficiency devices which device ordevices may receiving information in the packet, such as by using agroup ID, as discussed earlier. Thus, high-efficiency devices may beconfigured to receive and decode the L-STF 1405, L-LTF 1410, and L-SIG1415. If the L-SIG 1415 includes a one-bit code, high-efficiency devicesmay be configured to locate and decode the HE-SIG 1425 which is at ahigher frequency band, in order to determine whether the high-efficiencyportion of the hybrid packet contains information for that particulardevice.

In some aspects, the legacy packet may, as illustrated, take up only 20MHz of bandwidth. However, the legacy portion of the packet 1400 mayalso take up a different amount of bandwidth as well. For example, thelegacy portion of the hybrid packet may comprise a 40 MHz, 60 MHz, 80MHz or other size legacy packet, while the high-efficiency portion ofthe hybrid packet 1400 may use the remainder of the available bandwidth.In some aspects, channels of sizes other than 20 MHz may also be used.For example, channels may be 5, 10, 15, 40 MHz, or other sizes. In someaspects, following the legacy VHT-SIG-A 1420, a legacy packet 1430 maybe transmitted in a primary channel to a legacy device. In some aspects,the legacy packet 1430 may include at least the primary channel, and mayalso include additional channels. For example, this legacy packet 1430may be compatible with IEEE 802.11a, 802.11n, or 802.11ac devices. Insome aspects, following the one or more HE-SIGs 1425, a high-efficiencypacket 1435 may be transmitted to one or more high-efficiency devices,using at least a portion of the bandwidth available to the AP. In someaspects, the legacy packet may be sent to multiple legacy devices. Forexample, the hybrid packet may comprise a MU-MIMO 802.11ac packet, whichis sent to two or more 802.11ac-compatible STAs.

FIG. 15 illustrates an exemplary method 1500 of transmitting a hybridpacket. This method may be done by a wireless device, such as an AP.

At block 1505, the AP transmits to one or more first devices in a firstportion of a bandwidth, the one or more first devices having a first setof capabilities. In some aspects, the one or more first devices may belegacy devices. In some aspects, the first portion of the bandwidth maybe a primary channel. In some aspects, the means for transmitting to afirst device may be a transmitter.

At block 1510, the AP simultaneously transmits to one or more seconddevices in a second portion of the bandwidth, the one or more seconddevices having a second set of capabilities wherein the transmissioncomprises a preamble which includes an indication for devices with thesecond set of capabilities to locate a frequency band where symbolscontaining a set of transmission parameters for devices with the secondset of capabilities are sent, and where the indication is sent so as tohave no substantial impact on a preamble decoding of devices with thefirst set of capabilities. In some aspects, the means for transmittingto one or more second devices may be a transmitter. In some aspects, thepreamble may be a legacy preamble, and the indication may be a one-bitcode in an L-SIG in the legacy preamble. In some aspects, the indicationmay be contained in the L-SIG in the primary channel, in the primarychannel and one or more other channels, or in other channels.

FIG. 16 illustrates an exemplary method of receiving a hybrid packet. Insome aspects, this method may be used by a STA, such as ahigh-efficiency wireless communication device.

At block 1605, the STA receives a legacy preamble in a primary channel.In some aspects, the means for receiving a legacy preamble may be areceiver.

At block 1610, the STA determines whether the legacy preamble containsinformation sufficient to inform high-efficiency devices to locate ahigh-efficiency signal field in one or more non-primary channels. Insome aspects, the means for determining may be a processor or areceiver.

At block 1615, the STA receives the high-efficiency signal field in atleast one of the one or more non-primary channels. In some aspects, themeans for receiving the high-efficiency signal field may be a receiver.In some aspects, the STA may further receive data on at least one of theone or more non-primary channels. In some aspects, the means forreceiving data may be a receiver.

Delay Spread Protection and Potential Structures of a High-EfficiencySignal Field

In some aspects, outdoor or other wireless networks may have channelswith relatively high delay spreads, such as those in excess of 1 μs. Forexample, an access point at a high elevation, such as a pico/macro celltower access point, may have high delay spreads. Various wirelesssystems, such as those in accordance with 802.11a/g/n/ac, use a CyclicPrefix (CP) length of only 800 ns. Nearly half of this length may beconsumed by transmit and receive filters. Because of this relativelyshort CP length and the overhead from the transmit and receive filters,such 802.11a/g/n/ac networks may be unsuitable for an outdoor deploymentwith a high delay spread.

According to aspects of the present disclosure, a packet format (PHYwaveform) that is backwards compatible with such legacy systems andsupports cyclic prefixes longer than 800 ns is provided that may allowthe use of 2.4 and 5 GHz WiFi systems in outdoor deployments.

For example, one or more bits of information may be embedded in one ormore of an L-STF, an L-LTF, an L-SIG, or in another portion of a packetpreamble, such as an HE-SIG. These one or more bits of information maybe included for devices configured to decode them, as above, but may notimpact decoding by legacy (e.g., 802 11a/g/n/ac) receivers. These bitsmay include an indication of a packet which includes delay spreadprotection, in order to allow the use of such a packet in an outdoorsetting, or another setting with potentially high delay spread.

In some aspects, a number of methods may be used to provide delay spreadprotection or tolerance. For example, different transmission parametersmay be used to increase symbol duration (e.g., downclocking to decreasesample rate or increasing FFT length while maintaining the same samplerate). Increasing the symbol duration, such as by 2× or 4×, may increasetolerance to higher delay spreads.

In some aspects, an increased symbol duration may be signaled in a fieldof an L-SIG or an HE-SIG. In some aspects, other packets on the networkmay not contain the signaling for increased symbol duration, but ratherbe packets with a conventional or “normal” symbol duration. Preserving a“normal” symbol duration may be desirable in some instances becauseincreased symbol duration typically means increased FFT size and thusincreased sensitivity to frequency error and increased PAPR. Further,not every device in a network will need this increased delay spreadtolerance. Thus, in some cases, an increased FFT size may hurtperformance, and so it may be desirable for some packets to useconventional symbol duration.

Thus, in some aspects, all packets may contain an increased symbolduration after an L-SIG or HE-SIG field. In other aspects, only packetswhich include information signaling an increased symbol duration in anL-SIG or an HE-SIG may include an increased symbol duration. In someaspects, the signaling for an increased symbol duration may be containedwithin an HE-SIG, and L-SIG, a VHT-SIG-A, or another field in a packet.In some aspects, this signaling may be conveyed by, for example, aQ-BPSK rotation in a symbol of a SIG field, such as an L-SIG or anHE-SIG. In some aspects, this signaling may be conveyed by hidinginformation in an orthogonal rail, such as an imaginary axis, of a fieldof a packet.

In some aspects, increase symbol duration may be used for either or bothof uplink or downlink packets. For an uplink packet, an AP may signal inpreceding downlink packet that the uplink packet may be transmittedusing an increased symbol duration. For example, in an uplink OFDMApacket, the AP may send a tone allocation message which tells users touse longer symbol durations. In that case, the uplink packet itself maynot need to carry an indication indicating a particular symbol duration.In some aspects, a signal from the AP to a STA may inform the STA to usea particular symbol duration in all future uplink packets, unless toldotherwise.

In some aspects, such delay spread protection may be incorporated intohigh-efficiency packets such as those described above. The preambleformats presented herein provide a scheme in which delay spreadprotection may be included in packets, while allowing legacy devices todetect whether a packet is an 802.11n, 802.11a or 802.ac packet.

The preamble formats presented herein may preserve the L-SIG-baseddeferral as in an IEEE 802.11 ac (mixed mode preamble) packet. Having alegacy section of a preamble decodable by 802.11a/an/ac stations mayfacilitate mixing legacy and HE devices in the same transmission.Preamble formats provided herein may help provide protection on the HESIG, which may help achieve robust performance. For example, thesepreamble formats may help to reduce a SIG error rate to 1% or less inrelatively stringent standard test scenarios.

FIG. 17 illustrates a packet with one example HE preamble format, inaccordance with aspects of the present disclosure. The example HEpreamble format is compared with a VHT preamble format. As illustrated,the HE preamble format may include one or more signal (SIG) fieldsdecodable by a first type of device (e.g., 802.11a/ac/n devices) and oneor more SIG fields (HE-SIG1) decodable by a second type of devices(e.g., HE devices). As illustrated, 802.111/ac/n devices may defer basedon a duration field in the L-SIG. The L-SIG may be followed by arepeated high efficiency SIG (HE-SIG) field. As illustrated, after therepeated HE-SIG field, a device may already know if the packet it is aVHT packet, so there may be no problem with VHT-STF gain setting.

In the example format shown in FIG. 17, HE-SIG1 fields may be repeatedand preceded with a normal guard interval (GI), which gives protectionto HE-SIG1 for HE devices. Because of the repeated HE-SIG1, this packetmay have a lower signal-to-noise ratio operating point, and thus providemore robust protections from inter-symbol-interference (ISI). In someaspects, the L-SIG may transmit at 6 Mbps, as packet type detectionbased on Q-BPSK checks on 2 symbols after L-SIG may not be impacted.

Various techniques may be used to signal the HE packet to HE devices, asdiscussed above. For example, the HE packet may be signaled by placingan orthogonal rail indication in L-SIG, based on a CRC check in HE-SIG1,or based on the repetition of the HE-SIG1.

The delay spread protection on HE-SIG2 may take various forms. Forexample, HE-SIG2 may be transmitted over 128 tones (in 20 MHz) toprovide additional delay spread protection. This may result in a guardinterval of 1.6 us, but may require interpolation of channel estimatescalculated based on L-LTF, which would contain the traditional number oftones. As another example, HE-SIG2 may have the same symbol duration,but may be sent with a 1.6 us cyclic prefix. This may lead to morecyclic prefix overhead than the traditional value of 25%, but may notrequire interpolation. In one aspect, HE-SIG2 may also be sent over thefull bandwidth, rather than repeating every 20 MHz. This may requirethat bandwidth bits be placed in HE-SIG1, in order to indicate the fullbandwidth.

FIG. 18 illustrates a packet with another example HE preamble format, inaccordance with aspects of the present disclosure. As with FIG. 17, theexample HE preamble format is compared with a VHT preamble format. Asbefore, IEEE 802.11 a/ac/n devices may defer to the packet based on theduration field in the L-SIG. The L-SIG may be followed by a repeatedhigh efficiency SIG (HE-SIG) field. In the example format shown in FIG.18, the HE-SIG1 fields may be repeated but with the first HE-SIG1 fieldpreceded with a normal guard interval, while the second HE-SIG1 precedesa normal guard interval.

This repetition of HE-SIG1, with a guard interval placed before thefirst HE-SIG1 and after the second HE-SIG1 may provide protection for HEdevices. It may be noted that the middle portion of HE-SIG1 section mayappear as an HE-SIG1 symbol with a relatively large CP. In this aspect,a Q-BPSK check on the first symbol after L-SIG may be unaffected.However, a Q-BPSK check on the second symbol may give random results dueto the guard interval after the second HE-SIG1. However, these randomresults may not have an adverse impact on VHT devices. For example, VHTdevices may classify the packet as an 802.11ac packet, but at this pointthe devices may attempt to perform a VHT-SIG CRC check, and this willfail. Accordingly, VHT devices will still defer to this packet, despitethe random results of the Q-BPSK check on the second symbol after theL-SIG.

Because the auto-detection process for legacy devices, such as VHTdevices (those compatible with IEEE 802.11ac), will cause those devicesto defer to the packet in FIG. 18, these packets may still carry 6 Mbps.As with the packet in FIG. 17, a number of techniques discussed abovemay be used to signal to HE devices that the packet is an HE packet.Similarly, HE devices may be provided information about the delay spreadprotection of the packet in a number of ways, such as a field containedin HE-SIG2.

FIG. 19 illustrates a packet with another example HE preamble format, inaccordance with aspects of the present disclosure. As before, theexample HE preamble format is similar to an 802.11ac VHT preambleformat. As illustrated, 802.11a/ac/n devices may defer to the packetbased on the duration field in the L-SIG. The L-SIG may be followed by arepeated high efficiency SIG (HE-SIG) field.

In the example format shown in FIG. 19, repeated HE-SIG1 fields may bepreceded by a double guard interval (DGI). The use of such a doubleguard interval may result in a random result of a Q-BPSK check on thefirst symbol after the L-SIG. Thus, some legacy devices may not defer tothis packet if the L-SIG signals a rate of 6 Mbps. Accordingly, theL-SIG in such a packet may need to signal a rate other than 6 Mbps, inorder to ensure that all IEEE 802.11a/ac/n devices defer to the packet.For example, the L-SIG may signal a rate of 9 Mbps. Techniques similarto those discussed above may be used to signal that the packet is an HEpacket, and may be used to signal whether the packet contains delayspread protection.

Various optimization may be provided for preamble formats, such as thoseshown in FIGS. 17-19. For example, for the example formats shown inFIGS. 18 and 19, it may be possible to truncate the second HE-SIG1symbol and start the next symbol earlier, to save overhead. In addition,there may be some benefit to having a SIG-B after the HE-LTFs, which mayprovide per-user bits for MU-MIMO.

FIG. 20 illustrates example bit allocation for an HE-SIG 1 field. Asillustrated, there may be 2-3 bits for BW indication, an 8-bit Lengthindication, a bit to indicate longer symbols are used, 2-3 reservedbits, 4 bits for a CRC, and 6 tail bits. If a Longer Symbols ON bit isprovided in HE-SIG1, this may be used to signal either of the following:that HE-SIG2 has delay spread protection or everything after HE-SIG2uses an increased FFT size. The above HE-SIG formats, where HE-SIG ismade up of HE-SIG1 and HE-SIG2 may allow for delay spread protection,and may be used in packets which allow multiple access, such as OFDMApackets.

Uplink Packet with Legacy Preamble

FIG. 21 illustrates an exemplary structure of an uplink physical-layerpacket 2100 which may be used to enable backward-compatible multipleaccess wireless communications. Typically, in an uplink packet, a legacypreamble may not be needed, as the NAV is set by the AP's initialdownlink message. The AP's initial downlink message may cause legacydevices on the network to defer to the uplink packet. However, somewireless devices may be outside the range of the AP, but within therange of STAs that are transmitting to the AP. Accordingly, thesedevices, if they are legacy devices, may not defer to the AP as they didnot receive the AP's initial downlink message. These devices may alsonot defer to an uplink packet like those in FIG. 12, because thosepackets do not have a legacy preamble that legacy devices can recognize.Accordingly, the transmission of such a device may interfere with anuplink packet, and so it may be desirable to transmit an uplink packetwhich contains a legacy preamble sufficient to cause legacy devices todefer to the packet. These uplink packets may take a number of possibleforms. Uplink packet 2100 is an exemplary uplink packet which contains alegacy preamble. Note that while packet 2100 includes times for eachportion of the packet, these times are merely exemplary. Each portion ofthe packet 2100 may be longer or shorter than indicated. In someaspects, it may be beneficial for the legacy portions of the preamble,such as L-STF, L-LTF, and L-SIG to be the listed times, in order toallow legacy devices to decode the legacy portion of the preamble anddefer to the packet 2100.

Accordingly, the packet 2100 may be used to inform such legacy devicesto defer to the uplink packet, by providing a legacy preamble which suchlegacy devices may recognize. This legacy preamble may include an L-STF,an L-LTF, and an L-SIG. Each of the transmitting devices, as in thepacket 830, may be configured to transmit their own preamble on theirassigned bandwidth. These legacy preambles may protect the uplinkcommunications from nodes which did not hear the AP's initial downlinkmessage.

As in packet 830, each of a number of devices, here N devices, maytransmit in their assigned bandwidth simultaneously. Following thelegacy preamble, each device may transmit a high-efficiency preamble onits assigned tones. For example, each device may transmit an HE-SIG onits own assigned tones. Following this HE-SIG, each device may thentransmit an HE-STF, and may transmit one or more HE-LTFs. For example,each device may transmit a single HE-STF, but may transmit a number ofHE-LTFs which correspond to the number of spatial streams assigned tothat device. In some aspects, each device may transmit a number ofHE-LTFs corresponding to the number of spatial streams assigned to thedevice with the highest number of spatial streams. This assignment ofspatial streams may be done, for example, in the AP's initial downlinkmessage. If each device sends the same number of HE-LTFs, this mayreduce a peak-to-average-power ratio (PAPR). Such a reduction of PAPRmay be desirable. Further, if each device transmits the same number ofHE-LTFs, this may make processing the received uplink packet easier forthe AP. For example, if a different number of HE-LTFs are sent by eachdevice, the AP may receive the preamble for one device while receivingdata from another device. This may make decoding the packet more complexfor the AP. Accordingly, it may be preferable to use the same number ofHE-LTFs for each devices. For example, each of the transmitting devicesmay be configured to determine the maximum number of spatial streams anydevice is receiving, and to transmit a number of HE-LTFs correspondingto that number.

In some aspects, the L-STF in such a packet may include small cyclicshifts, on the order of approximately up to 200 ns. Large cyclic shiftsmay cause issues in such L-STFs with legacy devices which might use adetection algorithm based upon cross-correlation. The HE-STF in such apacket 2100 may include larger cyclic shifts, on the order ofapproximately 800 ns. This may allow for more accurate gain settings inthe AP which is receiving the uplink packet 2100.

FIG. 22 illustrates another exemplary structure of an uplinkphysical-layer packet 2200 which may be used to enablebackward-compatible multiple access wireless communications. This packet2200 may be similar to the packet 2100, however, in this packet 2200,each of the transmitting devices may not transmit an HE-STF. Instead,each of the transmitting devices may transmit an L-STF with largercyclic shifts, such as on the order of approximately 800 ns. While thismay impact legacy devices with cross-correlation packet detectors, thismay allow a packet to be shorter, as this may allow the transmittingdevices to not transmit an HE-STF. While packet 2200 includes times foreach portion of the packet, these times are merely exemplary, and eachportion of the packet may be longer or shorter than indicated. In someaspects, it may be beneficial for the legacy portions of the preamble,such as L-STF, L-LTF, and L-SIG to be the listed times, in order toallow legacy devices to decode the legacy portion of the preamble anddefer to the packet 2200.

In packet 2200, each device may transmit a number of HE-LTFscorresponding to the number of spatial streams assigned to that device.In some aspects, each device may instead transmit a number of HE-LTFscorresponding to the number of spatial streams assigned to the devicewhich is assigned the highest number of spatial streams. As discussedabove, such an approach may reduce PAPR.

In some aspects, longer symbol duration can provide delay spreadprotection and protection from timing offsets. For example, the devicestransmitting an uplink packet may not begin to transmit the packet atthe same time, but instead begin at slightly different times. A longersymbol duration may also aid the AP in interpreting the packet in suchinstances. In some aspects, devices may be configured to transmit with alonger symbol duration based on a signal in the AP's downlink triggermessage. In some aspects, for a green-field packet such as packet 830,the entire waveform may be transmitted at a longer symbol duration, asthere is no need for legacy compatibility. In an uplink packet whichincludes a legacy preamble, such as packet 2100 or 2200, the legacypreamble may be transmitted with a conventional symbol duration. In someaspects, the portion after the legacy preamble may be transmitted with alonger symbol duration. In some aspects, longer symbol duration may beachieved by using an existing IEEE 802.11 tone plan in a smallerbandwidth. For example, smaller sub-carrier spacing may be used, whichmay be referred to as down-clocking. For example, a 5 MHz portion ofbandwidth may use a 64-bit FFT 802.11a/n/ac tone plan, whereas 20 MHzmay be conventionally used. Thus, each tone may be 4× longer in such aconfiguration than in a typical IEEE 802.11a/n/ac packet. Otherdurations may also be used. For example, it may be desirable to usetones which are twice as long as in a typical IEEE 802.11a/n/ac packet.

FIG. 23 illustrates an exemplary method 2300 of receiving a packet. Thismethod may be done by a wireless device, such as an AP.

At block 2305, the AP receives a first portion in a first section of abandwidth, the first portion transmitted by a first wireless device, thefirst portion comprising a legacy section of a first preamble containinginformation sufficient to inform legacy devices to defer to the packetand a high-efficiency section of the first preamble. In some aspects,the means for receiving may be a receiver.

At block 2310, the AP simultaneously receives a second portion in asecond section of the bandwidth, the second portion transmitted by asecond wireless device, the second portion comprising a legacy sectionof a second preamble containing information sufficient to inform legacydevices to defer to the packet and a second high-efficiency section ofthe second preamble. In some aspects, the means for simultaneouslyreceiving may be a receiver. In some aspects, the first wireless deviceand/or the second wireless device may transmit on a number of spatialstreams. In some aspects, the high-efficiency portion of the preambletransmitted by the first and second wireless devices may contain anumber of long training fields. In some aspects, the number of longtraining fields can be based on the number of spatial streams assignedto that particular device or the highest number of spatial streamsassigned to any wireless device.

In some aspects, it may be desirable for an uplink OFDMA packet to havea structure which more closely mimics that of an uplink multi-usermultiple input and multiple-output (MU-MIMO) packet. For example, anumber of the preceding packets, such as packet 2100 in FIG. 21, mayinclude an HE-SIG prior to one or more HE-LTFs. Similarly, in packet 830in FIG. 12, each of the transmitting devices transmits a single HE-LTF,followed by an HE-SIG, followed by the remaining number of HE-LTFs.However, in order to have an uplink packet with a structure more similarto the of an uplink MU-MIMO packet, it may be desirable to have a packetin which the HE-SIG follows after all of the HE-LTFs in the packet.

Accordingly, in any of the packets described, it may be possible totransmit the HE-SIG following all of the HE-LTFs. In some aspects, itmay be desirable to find another method of signaling the number ofspatial streams being used by each transmitting device in the uplinkpacket when the HE-SIG follows after all of the HE-LTFs. For example, insome of the previously-described packets, the first HE-LTF from atransmitting device may include information sufficient to allow the APto decode the HE-SIG from that transmitting device. In some of thepreviously-described packets, the HE-SIG from a transmitting device mayinclude information regarding the number of spatial streams which arebeing used by that device in the packet, and thus, in some aspects, theHE-SIG may indicate the number of HE-LTFs which will be transmitted bythat transmitting device. However, if an HE-SIG is transmitted followingeach HE-LTF, it may be desirable to indicate the number of spatialstreams used by a transmitting device in a different manner than this.For example, the number of spatial streams used by a transmitting devicemay be indicated in a downlink message from the AP. For example, theuplink OFDMA packet may be sent in response to a downlink packet fromthe AP, which indicates which devices may transmit on the uplink OFDMApacket. Accordingly, this downlink packet may also assign a number ofspatial streams to each device.

FIG. 24 is an exemplary uplink packet structure in which the HE-SIG istransmitted after each HE-LTF. In uplink OFDMA packet 2400, each of thetransmitting devices may transmit an HE-STF 2410, as in other packetsdescribed above. Following the HE-STF 2410, each of the transmittingdevices may transmit a number of HE-LTFs 2420. Each of the transmittingdevices may transmit a number of HE-LTFs 2420 which corresponds to thenumber of spatial streams which are being used by that transmittingdevice. For example, if a transmitting device is transmitting using twospatial streams, that device may transmit two HE-LTFs 2420. Followingtransmitting all of its HE-LTFs 2420, each transmitting device thentransmit an HE-SIG 2430. This HE-SIG 2430 may contain informationsimilar to that described above.

As illustrated, in packet 2400, each transmitting device transmits anumber of HE-LTFs 2420 which corresponds to the number of spatialstreams being used by that device. As discussed above, in some otheraspects, the number of spatial streams being used by a device may beindicated in the HE-SIG sent by that device. However, in packet 2400,the number of spatial streams may not be included in the HE-SIG 2430, asthis indication may arrive too late for an AP to anticipate the numberof HE-LTFs 2420 that the transmitting device may transmit. Accordingly,other methods for the AP to determine the number of spatial streams froma given event may be used. For example, a downlink message from the AP,such as the message triggering the uplink OFDMA packet 2400, may assigna number of spatial streams to each transmitting device. An exemplarydownlink message from the AP is illustrated in FIG. 26 which includesinformation on how many spatial streams each transmitting device mayuse. In some aspects, the number of spatial streams used by eachtransmitting device may be determined in other ways as well. Forexample, the number of spatial streams to each transmitting device maybe conveyed in a periodic downlink message, such as in a beacon. In someaspects, the AP may be configured to determine the number of spatialstreams based upon the received packet 2400. For example, the AP may beconfigured to determine the number of HE-LTFs 2420 being transmitted byeach transmitting device without prior knowledge of how many spatialstreams may be transmitted such as by analyzing the incoming packet 2400and detecting the end of the HE-LTFs 2420 and the beginning of theHE-SIG 2430. Other methods may also be used to enable the AP todetermine the number of spatial streams, and thus the number of HE-LTFs2420 being transmitted by each device in packet 2400. Following theHE-SIG 2430 from each transmitting device, that device may transmit thedata 2440 which it wishes to transmit in packet 2400. In some aspects,each device may transmit the same number of HE-LTFs 2420 in packet 2400.For example, each transmitting device may transmit a number of HE-LTFs2420 which corresponds to the number of spatial streams assigned to thedevice which is assigned the highest number of spatial streams.

FIG. 25 is another exemplary uplink packet structure in which the HE-SIGis transmitted after each HE-LTF. Packet 2500 may correspond to amixed-mode packet, in which each transmitting device transmits a legacypreamble prior to transmitting a high-efficiency portion of the packet.In packet 2500, each device first transmits a legacy preamble, whichincludes an L-STF 2502, and L-LTF 2504, and an L-SIG 2506. Theseportions of the packet 2500 may be transmitted as described above.

Following the legacy preamble, packet 2500 is similar to packet 2400.Each of the transmitting devices may transmit an HE-STF 2510, followedby a number of HE-LTFs 2520, followed by an HE-SIG 2530, followed by thedata 2540 which the transmitting device wishes to transmit to the AP.Each of these portions of the packet may be transmitted in methodssimilar to those disclosed above. The number of HE-LTFs 2520 transmittedby each device may be based, at least in part, on the number of spatialstreams that each device is transmitting on. For example, a device whichis transmitting on two spatial streams may transmit two HE-LTFs 2520.

In some aspects, each device in packet 2500 may transmit an equal numberof HE-LTFs 2520. For example, each of the transmitting devices maytransmit a number of HE-LTFs 2520 which corresponds to the highestnumber of spatial streams being transmitted by any of the transmittingdevices. Accordingly, in packet 2500, each of the transmitting devicesmust have knowledge of how many HE-LTFs 2520 to transmit in the packet.As before, having each of the transmitting devices transmit the samenumber of HE-LTFs 2520 may be beneficial, as this may reduce the PAPR ofthe packet. Such a reduction in PAPR may result in benefits for the APreceiving the packet 2500, as described above. If each transmittingdevice in packet 2500 transmits the same number of HE-LTFs 2520, each ofthese devices should be aware of how many HE-LTFs 2520 to transmit. Thismay be accomplished in a number of ways. For example, the AP may send adownlink trigger message to the transmitting devices. This triggermessage may include information such as which devices may transmit inthe uplink packet, the bandwidth assigned to each device, and the numberof spatial streams assigned to each device. This trigger message mayalso indicate to the transmitting devices how many HE-LTFs 2520 toinclude in the uplink packet 2500. For example, the downlink message mayindicate to the transmitting devices how many spatial streams eachdevice may use. An exemplary downlink trigger message from the AP isillustrated in FIG. 26 which includes information on how many spatialstreams each transmitting device may use. Similarly, the number ofspatial streams assigned to each device may be fixed. For example, anetwork may be constructed in which each device may use only two spatialstreams. Similarly, the number of spatial streams assigned to eachdevice may be conveyed in a message such as in a beacon message which isperiodically transmitted from the AP. Accordingly, the transmittingdevices may transmit a number of HE-LTFs 2520 which corresponds to thenumber of spatial streams assigned to the device which is assigned themost spatial streams. In some aspects, other methods may also be used tocoordinate the number of HE-LTFs 2520 transmitted by each transmittingdevice.

An exemplary downlink message 2600 from the AP is illustrated in FIG. 26which includes information on how many spatial streams each transmittingdevice may use. This message 2600 may include trigger messageinformation 2605. For example, this information 2605 may include timinginformation on when an uplink message may be sent. This information 2605may further include information regarding whether the transmittingdevices should confirm receipt of the trigger message. Following thisinformation 2605, the downlink message 2600 may include anidentification 2610 of device 1. This identification 2610 may be, forexample, a unique number or value which is assigned to device 1, andwhich identifies device 1. The downlink message 2600 may also include anumber of streams 2615 which are assigned to device 1. For example,device 1 may be assigned two spatial streams. The downlink message mayalso include an identification 2620 of device 2, a number of spatialstreams 2625 for device 2, an identification 2630 of device 3, and anumber of spatial streams 2635 for device 3. In some aspects, othernumbers of devices may also be identified in a downlink message 2600.For example, two, three, four, five, six or more devices may beidentified in the downlink message 2600. Note that this downlink message2600 is merely exemplary. Other information may also be contained in adownlink trigger message, and may be contained in a different order ornumber than illustrated in downlink message 2600.

In some aspects, it may be beneficial to harmonize the LTFs which aretransmitted in an uplink OFDMA packet with those transmitted in an ULMU-MIMO packet. For example, in an UL MU-MIMO packet, each transmittingdevice may transmit messages across all tones. Accordingly, the LTFs inan UL MU-MIMO packet may need to contain sufficient information to allowa receiving STA, such as an AP, to recognize the transmissions from eachtransmitting STA on each tone. Such LTF formats may be used both in anUL MU-MIMO packet, and in an UL OFDMA packet.

For example, one format that may be used for LTFs, in either an ULMU-MIMO packet or an UL OFDMA packet, is to transmit P-matrix basedLTFs. In this approach, LTFs may be transmitted by each of thetransmitting STAs on each tone. The LTFs from each device may betransmitted in such a way that they are orthogonal to each other. Thenumber of LTFs transmitted may correspond to the number of spatialstreams assigned to all devices. For example, if two devices transmit onone stream each, two LTFs may be sent. In some aspects, in the firstLTF, the value at a given tone may be equal to H1+H2, where H1 is thesignal from the first device and H2 is the signal from the seconddevice. In a next LTF, the value at a given tone may be equal to H1−H2.Accordingly, because of this orthogonality, the receiving device may beable to identify the transmission of each of the two transmittingdevices on each tone. Such a format for LTFs has been used, for example,in previous IEEE 802.11 formats. However, one potential problem with Pmatrix based LTFs is that they may not be as effective if two or more ofthe transmitting devices have a high frequency offset with respect toone another. In that circumstance, the orthogonally of the LTFs may belost, and accordingly, the ability of the receiving device to properlydecode the packet may be impaired. Accordingly, in some aspects, it maybe desirable to use a different LTF format for UL MU-MIMO and UL OFDMApackets.

Another possible different LTF format for UL MU-MIMO and UL OFDMApackets is to use a tone-interleaved or sub-band interleaved LTF. Asbefore, the number of LTFs which is transmitted may correspond to thetotal number of spatial streams sent by all transmitting devices. SuchLTF formats may be especially useful when there is a big frequencyoffset among the various devices transmitting the uplink packet. TheseLTF formats could be used in an UL MU-MIMO packet. In order to harmonizean UL OFDMA packet with an UL MU-MIMO packet, these LTF formats may alsobe used in an UL OFDMA packet.

FIG. 27 is an illustration 2700 of a tone-interleaved LTF which may beused in an UL OFDMA packet. For example, these LTFs may be used in anyof the previously described UL OFDMA packets. For example, in thispacket, there are four spatial streams. These spatial streams may benumbered, for example, as spatial stream 1-4. Each spatial stream may betransmitted by a separate device, or one device may transmit two or moreof the spatial streams. Accordingly, four spatial streams may correspondto an UL OFDMA packet which is being transmitted by two, three, or fourdevices. Because four spatial streams are present, four LTFs may besent, labeled LTF1 2705, LTF2 2710, LTF3 2715, and LTF4 2720. Each LTFmay include a number of tones, here numbered from 1 to 8. Any number oftones may be included in the LTF, corresponding to the number of toneswhich are included in the data portion of the UL OFDMA packet. In thistone-interleaved LTF, during LTF1 2705, the first stream may transmit ontones 1, 5, 9, and so on. In some aspects, the spacing between thesetones (that is, the spacing between 1 and 5) is based on the number ofspatial streams. For example, in the illustration 2700 there are fourspatial streams and so the spacing between tones which each streamtransmits on is also four. During LTF1 2705, the second stream maytransmit on tones 2, 6, 10, and so on, while the third spatial streammay transmit on tones 3, 7, 11 and so one, and the fourth spatial streammay transmit on tones 4, 8, 12, and so on. In a next LTF, LTF2 2710,each spatial stream may transmit on tones which are 1 tone higher thanthe previous LTF. For example, in LTF1 2705, stream 1 transmitted ontones 1 and 5, while in LTF2 2710, stream 1 transmits on tones 2 and 5.Accordingly, after a number of LTFs equal to the number of spatialstreams, each spatial stream may have transmitted on each tone. Usingthis tone-interleaved LTF, since spatial streams do not transmit at thesame frequency at the same time, cross-stream leakage may not be anissue because of the offset. For example, the offset may be a few kHz.In some aspects, it may be advantageous to repeat LTF1 2725 again afterthe last LTF, in order to estimate per-stream frequency offset. Forexample, LTF1 2705 may be identical to LTF1 2725. However, these twoLTFs may be compared to

FIG. 28 is an illustration 2800 of a sub-band interleaved LTF which maybe used in an UL OFDMA packet. For example, these LTFs may be used inany of the previously described UL OFDMA packets. The UL OFDMA packetmay include a number of spatial streams, and may be transmitted on anumber of tones. For example, illustration 2800 includes four spatialstreams. Because there are four spatial streams, the tones, from 1 toN_(SC), where N_(SC) is the total number of subcarriers excluding guardtones and DC tones, are divided into four sub-bands. For example, ifthere were 64 tones, tones 1-16 could be sub-band 1, tones 17-32 couldbe sub-band 2, tones 33-48 could be sub-band 3 and tones 49-64 could besub-band 4. In some aspects, the number of tones in each sub-band may beequal or may be approximately equal. In each of the four LTFs, each ofthe four spatial streams may transmit on the tones of its assignedsub-band. For example, in LTF1 2805, sub-band 1 may be assigned tospatial stream 1, sub-band 2 may be assigned to spatial stream 2, and soone. In the subsequent LTF2 2810, each of the sub-bands may be assignedto a different one of the spatial streams. Accordingly, after four LTFs,each of the four spatial streams may have transmitted once on each ofthe four sub-bands.

The LTF structures illustrated in illustration 2700 and illustration2800 may have a number of advantages. For example, this structure mayoffer better performance when there is a large frequency offset betweenuplink clients. Further, these LTF structures will allow the AP toreceive transmissions in each of the spatial streams on each of thetones. This may allow, for example, a spatial stream to switch fromcertain tones to certain other tones if such a switch was desired.Further, this may allow the AP to determine the signal strength of agiven spatial stream of a given device on each tone. This may allow theAP, in a future packet, to assign tones to a device based on which tonesthat device has the best signal. For example, if the AP assigns tones tovarious devices, the AP may observe that a certain device has a lowersignal-to-noise ratio and a stronger signal on some tones over othertones. Accordingly, the AP may assign that device those stronger tonesin a future packet. FIG. 29 is an exemplary LTF portion 2900 of a packetwhich may be transmitted in an UL OFDMA packet. For example, asdescribed above, in certain UL OFDMA packets, rather than allocatingtones in a SIG portion of the packet, tones may be allocated elsewhere.For example, as described above, certain UL OFDMA packets may allocatetones in a signaling message from the AP to the transmitting devices,which may allocate certain tones to certain devices. Thus, while inprevious UL packets, the SIG may include MCS, coding bits, and toneallocation information, in some aspects, the tone allocation informationneed not be included in a SIG field. Thus, it may be that a SIG fieldcould include only MCS and coding bits, which together comprise 6-7 bitsof information, and binary convolutional coding (BCC) tail bits, whichmay be six bits. Accordingly, it may be inefficient to transmit a SIGfield which includes only 6-7 bits of information, when transmittingsuch a SIG field also includes 6 bits of CRC information as overhead.Further, it is not clear whether including such CRC information hassufficient benefits in this case at all. Thus, it may be desired to sendan LTF portion 2900 of a packet which includes the MCS information 2910and coding bits 2915. By including this information in an LTF portion ofthe packet, the packet may not need to include a SIG field at all.

This information may be included in the LTF portion 2900 of the packetin a number of ways. For example, signaling mechanisms which can usenon-coherent demodulation may be used. In some aspects, the MCSinformation 2910 and coding bits 2915 may be includes in a low-strengthcode across some or all of the tones of the LTF. In some aspects, theMCS information 2910 and coding bits 2915 may be transmitted in a singleLTF, such as in LTF1 2825 or another LTF. In some aspects, the MCSinformation 2910 and coding bits 2915 may be split across each of themultiple LTFs. For example, one or more bits of the MCS information 2910and coding bits 2915 may be includes in two or more of the LTFs.Accordingly, in some aspects, an explicit SIG field may be needed in anUL OFDMA packet, as this information may be contained within the LTFs ofthe packet.

Typically, in an UL MU-MIMO packet, a per-user SIG field may be includedafter each of the LTFs for that packet have been transmitted. Forexample, this format may be similar to that of packet 2400. However, inan UL OFDMA packet, the HE-SIG may be included prior to the STFs or LTFsof a packet, as illustrated in packet 2100. In some aspects, in order toharmonize an UL MU-MIMO packet with an UL OFDMA packet, it may bedesirable to transmit a packet with a SIG field in both locations. Forexample, a packet may be transmitted which includes a common SIG field,prior to the HE-STF, and also includes a per-user SIG field after all ofthe HE-LTFs.

FIG. 30 is an illustration of a packet 3000 with a common SIG fieldprior to the HE-STF and per-user SIG field after all of the HE-LTFs. Inpacket 3000, the packet is shown to include a legacy preamble, include alegacy short training field 3005, a legacy long training field 3010, anda legacy SIG field 3015. However, this packet may also be transmittedwithout such a legacy preamble. Following the legacy preamble, if such apreamble is include, the packet 3000 includes a common SIG 3020. In someaspects, this common SIG 3020 may include information similar to thatincluded in such a SIG field in previous UL OFDMA packets. For example,the common SIG may carry the number of spatial streams included in theOFDMA packet. For example, each transmitting device in an UL OFDMApacket may popular a portion of the tones of the Common SIG 3020.Following the Common SIG 3020, an HE-STF 3025 and HE-LTFs 3030 aretransmitted. These fields may be transmitted according to the abovedisclosures. For example, the HE-LTFs 3030 may be based upon the LFTformats illustrated in FIGS. 27 and 28. Any number of HE-LTFs 3030 maybe transmitted. For example, the number of HE-LTFs 303 which aretransmitted may be based, at least in part, on the sum of the number ofspatial streams which are a part of the packet 3000. Following theHE-LTFs 303, a second SIG field may be transmitted. This per-user SIG3035 may be transmitted by each of the devices transmitting the UL OFDMApacket. The format of the per-user SIG field 3035 may be based upon theformat of the SIG field in a UL MU-MIMO packet. Following the per-userSIG field 3035, data 3040 may be transmitted. Accordingly, packet 3000may include both the Common SIG 3020, as in other UL OFDMA packets, anda per-user SIG field 3035, as in other UL MU-MIMO packets. Because bothSIG fields are included in packet 3000, this packet format may be reusedin both UL OFDMA and UL MU-MIMO.

FIG. 31 illustrates an exemplary method 3100 of transmitting to one ormore devices in a single transmission. This method may be done by awireless device, such as an AP.

At block 3105, the AP transmits a first section of a preamble accordingto a first format, the first section of the preamble containinginformation sufficient to inform devices compatible with the firstformat to defer to the transmission. For example, the first format maybe a pre-existing format, such as a format defined by one or more of theexisting IEEE 802.11 standards. In some aspects, the first format may bereferred to as a legacy format. In some aspects, the first section ofthe preamble may contain information sufficient to alert devices with asecond set of capabilities and/or compatible with a second format thatanother section of the preamble may be transmitted to those devices. Insome aspects, the means for transmitting the first section may include atransmitter.

At block 3110, the AP transmits a second section of the preambleaccording to a second format, the second section of the preamblecontaining tone allocation information, the tone allocation informationidentifying two or more wireless communication devices. For example, thesecond section of the preamble may comprise a high-efficiency preamble,and the second format may include an IEEE 802.11 format which is newerthan the first format. In some aspects, the second section of the AP mayidentify two or more wireless communication devices and may assign eachof those devices one or more sub-bands of the bandwidth of thetransmission. In some aspects, the means for transmitting the secondsection may include a transmitter.

At block 3115, the AP transmits data to the two or more wirelesscommunication devices simultaneously, the data contained on two or moresub-bands. In some aspects, each of the sub-bands may be transmitted onseparate and distinct non-overlapping portions of the bandwidth of thetransmission. For example, each sub-band may correspond to a certainportion of the bandwidth of the transmission, and each wirelesscommunication device may be assigned to receive data on one or more ofthe sub-bands. Accordingly, the AP may transmit different data to two ormore different wireless communication devices at the same time, indifferent sub-bands of the bandwidth of the transmission. In someaspects, the means for transmitting data may include a transmitter.

FIG. 32 illustrates an exemplary method 3200 of transmitting to one ormore first devices with a first set of capabilities and simultaneouslytransmitting to one or more second devices with a second set ofcapabilities. This method may be done by a wireless device, such as anAP.

At block 3205, the AP transmits to one or more first devices in a firstportion of a bandwidth, the one or more first devices having a first setof capabilities. In some aspects, this transmission may occur on aprimary channel and may also occur on one or more secondary channels ofa given bandwidth. In some aspects, the devices with the first set ofcapabilities may include devices which are compatible with certain IEEE802.11 standards.

A block 3210, the AP simultaneously transmits to one or more seconddevices in a second portion of the bandwidth, the one or more seconddevices having a second set of capabilities wherein the transmissioncomprises a preamble which includes an indication for devices with thesecond set of capabilities to locate a frequency band in the bandwidthfor symbols containing a set of transmission parameters for devices withthe second set of capabilities, and where the indication is sent so asto have no substantial impact on a preamble decoding of devices with thefirst set of capabilities. For example, the indication may be a one-bitcode which is on an imaginary axis of a portion of the preamble. Thisindication may be sent with low power, such that it may not interferewith the reception of the preamble by devices with the first set ofcapabilities. In some aspects, the second set of capabilities may benewer and more advanced than the first set of capabilities. For example,the first set of capabilities may correspond to a “legacy” format, whilethe second set of capabilities may correspond to a “high-efficiency”format. In some aspects, the devices with the second set of capabilitiesmay be configured to look for the indication in a transmission, and ifthe indication is found, may be configured to locate and receive theportion of the transmission contained in the second portion of thebandwidth. In some aspects, the transmission in the second portion ofthe bandwidth may correspond to various types of high-efficiency packetsdescribed above.

In some aspects, the indication may be included as a one-bit code in thepreamble. In some aspects, the preamble may be transmitted, induplicate, across a bandwidth of the transmission. In some aspects, theindication may be included in certain portions of this preamble. Forexample, the indication may be included in the copies of the preamblewhich are transmitted in portions of the bandwidth which will containtransmissions to devices having the second set of capabilities. In someaspects, the means for transmitting to one or more first devices and themeans for simultaneously transmitting to one or more second devices mayinclude a transmitter.

FIG. 33 illustrates an exemplary method 3300 of receiving a transmissioncompatible with both devices with a first set of capabilities anddevices with a second set of capabilities. This method may be done by awireless device, such as a STA with the second set of capabilities.

At block 3305, the STA receives a preamble in a first portion of abandwidth, the preamble transmitted in a format compatible with deviceshaving a first set of capabilities. In some aspects, the first portionof the bandwidth may include a primary channel and may optionallyinclude one or more secondary channels. In some aspects, the first setof capabilities may include an IEEE 802.11 standard, such as IEEE802.11a or 802.11ac. In some aspects, the means for receiving thepreamble may include a receiver.

At block 3310, the STA determines whether the preamble containsinformation sufficient to inform devices having a second set ofcapabilities to locate a signal field in a second portion of thebandwidth, the second portion of the bandwidth not overlapping with thefirst portion of the bandwidth. For example, as indicated above, thepreamble may contain an indication such as a one-bit code on animaginary axis in at least a portion of the preamble. Accordingly, theSTA may be configured to determine whether or not this information ispresent in a given preamble. In some aspects, the second portion of thebandwidth may include one or more secondary channels. In some aspects,the means for determining whether the preamble contains the informationmay include a processor or a receiver.

At block 3315, the STA receives the signal field in the second portionof the bandwidth. For example, the indication may provide the STA withenough information to locate the second portion of the bandwidth, and tobe aware that a signal field will be transmitted in the second portionof the bandwidth. Thus, the STA may be configured to receive the signalfield in this portion of the bandwidth. In some aspects, the signalfield may be all or part of a preamble, such as a “high-efficiency”preamble which is transmitted to devices with the second set ofcapabilities in the second portion of the bandwidth. In some aspects,this may allow devices with the second set of capabilities to receiveinformation from an AP or another device on portions of the bandwidthwithout interrupting the reception of devices with the first set ofcapabilities on the first portion of the bandwidth. Accordingly, asdiscussed above, this may allow for more efficient use of the bandwidththat is available to an AP or another device, as this may allow forfuller use of the bandwidth more of the time. In some aspects, the meansfor receiving the signal field may include a receiver.

FIG. 34 illustrates an exemplary method 3300 of receiving atransmission, where portions of the transmission are transmitted bydifferent wireless devices. The method may be done by a wireless device,such as an AP.

At block 3405, the AP receives a first portion of the transmission in afirst section of a bandwidth, the first portion transmitted by a firstwireless device and including a first preamble and a first data section.In some aspects, the AP may have previously sent a message to the firstwireless device, informing the first wireless device of a time and abandwidth that it may transmit to the AP.

At block 3410, the AP simultaneously receives a second portion of thetransmission in a second section of the bandwidth, the second section ofthe bandwidth not overlapping with the first section of the bandwidth,the second portion transmitted by a second wireless device, the secondportion including a second preamble and a second data section. In someaspects, the first preamble and the second preamble may each containtraining fields. In some aspects, the number of training fields thateach preamble contains may be based on the number of spatial streamsassigned to a particular device. For example, a device that is assignedthree spatial streams may transmit one short training field, andtransmit three long-training fields. Similarly, a device assigned onespatial stream may transmit one short training field and one longtraining field. In some aspects, each device may transmit a number oftraining fields based on how many spatial streams were assigned to thatparticular device. In some aspects, it may be advantageous for eachdevice to transmit the same number of spatial streams. For example, ifeach device transmits the same number of spatial streams, this mayreduce peak-to-average power ratio of the combined transmission, whichmay be advantageous. In some aspects, the transmissions from the firstand second wireless devices may be triggered by a message from the AP.This message may also indicate to each device how many spatial streamsthat device may transmit on, and may indicate the number of trainingfields that each device should transmit.

FIG. 35 illustrates various components that may be utilized in awireless device 3502 that may be employed within the wirelesscommunication system 100. The wireless device 3502 is an example of adevice that may be configured to implement the various methods describedherein. For example, the wireless device 3502 may comprise the AP 104 orone of the STAs 106 of FIG. 10. In some aspects, the wireless device3502 may comprise a wireless device that is configured to receive thepackets described above.

The wireless device 3502 may include a processor 3504 which controlsoperation of the wireless device 3502. The processor 3504 may also bereferred to as a central processing unit (CPU). Memory 3506, which mayinclude both read-only memory (ROM) and random access memory (RAM),provides instructions and data to the processor 3504. A portion of thememory 3506 may also include non-volatile random access memory (NVRAM).The processor 3504 typically performs logical and arithmetic operationsbased on program instructions stored within the memory 3506. Theinstructions in the memory 3506 may be executable to implement themethods described herein. For example, the memory 3506 may containinstructions sufficient to allow the wireless device 3502 to receivetransmissions from high-efficiency devices. For example, the memory 3506may contain instructions sufficient to allow the wireless device 3502 toreceive packets which include a preamble for device with a first set ofcapabilities, and a second preamble for devices with a second set ofcapabilities. In some aspects, the wireless device 3502 may include aframe receiving circuit 3521, which may contain instructions sufficientto allow the wireless device 3502 to receive packets as described inmethod 3300 and/or method 3400. This frame receiving circuit 3521 maycontain instructions sufficient to allow a device to receive a preamblein a first portion of the bandwidth, determine if an indication ispresent, and receive a signal field in a second portion of thebandwidth, as describe in method 3300. In some aspects, the framereceiving circuit 3521 may contain instructions sufficient to allow adevice to receive a first portion of the transmission in a first secondof a bandwidth, and to simultaneously receive a second portion of thetransmission in a second section of the bandwidth, as described inmethod 3400.

The processor 3504 may comprise or be a component of a processing systemimplemented with one or more processors. The one or more processors maybe implemented with any combination of general-purpose microprocessors,microcontrollers, digital signal processors (DSPs), field programmablegate array (FPGAs), programmable logic devices (PLDs), controllers,state machines, gated logic, discrete hardware components, dedicatedhardware finite state machines, or any other suitable entities that canperform calculations or other manipulations of information.

The processing system may also include machine-readable media forstoring software. Software shall be construed broadly to mean any typeof instructions, whether referred to as software, firmware, middleware,microcode, hardware description language, or otherwise. Instructions mayinclude code (e.g., in source code format, binary code format,executable code format, or any other suitable format of code). Theinstructions, when executed by the one or more processors, cause theprocessing system to perform the various functions described herein.

The wireless device 3502 may also include a housing 3508 that mayinclude a transmitter 3510 and a receiver 3512 to allow transmission andreception of data between the wireless device 3502 and a remotelocation. The transmitter 3510 and receiver 3512 may be combined into atransceiver 3514. An antenna 3516 may be attached to the housing 3508and electrically coupled to the transceiver 3514. The wireless device3502 may also include (not shown) multiple transmitters, multiplereceivers, multiple transceivers, and/or multiple antennas.

The wireless device 3502 may also include a signal detector 3518 thatmay be used in an effort to detect and quantify the level of signalsreceived by the transceiver 3514. The signal detector 3518 may detectsuch signals as total energy, energy per subcarrier per symbol, powerspectral density and other signals. The wireless device 3502 may alsoinclude a digital signal processor (DSP) 3520 for use in processingsignals. The DSP 3520 may be configured to generate a data unit fortransmission. In some aspects, the data unit may comprise a physicallayer data unit (PPDU). In some aspects, the PPDU is referred to as apacket.

The wireless device 3502 may further comprise a user interface 3522 insome aspects. The user interface 3522 may comprise a keypad, amicrophone, a speaker, and/or a display. The user interface 3522 mayinclude any element or component that conveys information to a user ofthe wireless device 3502 and/or receives input from the user.

The various components of the wireless device 3502 may be coupledtogether by a bus system 3526. The bus system 3526 may include a databus, for example, as well as a power bus, a control signal bus, and astatus signal bus in addition to the data bus. Those of skill in the artwill appreciate the components of the wireless device 3502 may becoupled together or accept or provide inputs to each other using someother mechanism.

Although a number of separate components are illustrated in FIG. 35, oneor more of the components may be combined or commonly implemented. Forexample, the processor 3504 may be used to implement not only thefunctionality described above with respect to the processor 3504, butalso to implement the functionality described above with respect to thesignal detector 3518 and/or the DSP 3520. Further, each of thecomponents illustrated in FIG. 35 may be implemented using a pluralityof separate elements. Furthermore, the processor 3504 may be used toimplement any of the components, modules, circuits, or the likedescribed below, or each may be implemented using a plurality ofseparate elements. As used herein, the term “determining” encompasses awide variety of actions. For example, “determining” may includecalculating, computing, processing, deriving, investigating, looking up(e.g., looking up in a table, a database or another data structure),ascertaining and the like. Also, “determining” may include receiving(e.g., receiving information), accessing (e.g., accessing data in amemory) and the like. Also, “determining” may include resolving,selecting, choosing, establishing and the like. Further, a “channelwidth” as used herein may encompass or may also be referred to as abandwidth in certain aspects.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: a, b, or c” is intended to cover: a, b, c,a-b, a-c, b-c, and a-b-c.

The various operations of methods described above may be performed byany suitable means capable of performing the operations, such as varioushardware and/or software component(s), circuits, and/or module(s).Generally, any operations illustrated in the Figures may be performed bycorresponding functional means capable of performing the operations.

The various illustrative logical blocks, modules and circuits describedin connection with the present disclosure may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array signal (FPGA) or other programmable logic device(PLD), discrete gate or transistor logic, discrete hardware componentsor any combination thereof designed to perform the functions describedherein. A general purpose processor may be a microprocessor, but in thealternative, the processor may be any commercially available processor,controller, microcontroller or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

In one or more aspects, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium.Computer-readable media includes both computer storage media andcommunication media including any medium that facilitates transfer of acomputer program from one place to another. A storage media may be anyavailable media that can be accessed by a computer. By way of example,and not limitation, such computer-readable media can comprise RAM, ROM,EEPROM, CD-ROM or other optical disk storage, magnetic disk storage orother magnetic storage devices, or any other medium that can be used tocarry or store desired program code in the form of instructions or datastructures and that can be accessed by a computer. Also, any connectionis properly termed a computer-readable medium. For example, if thesoftware is transmitted from a website, server, or other remote sourceusing a coaxial cable, fiber optic cable, twisted pair, digitalsubscriber line (DSL), or wireless technologies such as infrared, radio,and microwave, then the coaxial cable, fiber optic cable, twisted pair,DSL, or wireless technologies such as infrared, radio, and microwave areincluded in the definition of medium. Disk and disc, as used herein,includes compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk and blu-ray disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Thus, in some aspects computer readable medium may comprisenon-transitory computer readable medium (e.g., tangible media). Inaddition, in some aspects computer readable medium may comprisetransitory computer readable medium (e.g., a signal). Combinations ofthe above should also be included within the scope of computer-readablemedia.

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

The functions described may be implemented in hardware, software,firmware or any combination thereof. If implemented in software, thefunctions may be stored as one or more instructions on acomputer-readable medium. A storage media may be any available mediathat can be accessed by a computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code in the form of instructions or datastructures and that can be accessed by a computer. Disk and disc, asused herein, include compact disc (CD), laser disc, optical disc,digital versatile disc (DVD), floppy disk, and Blu-ray® disc where disksusually reproduce data magnetically, while discs reproduce dataoptically with lasers.

Thus, certain aspects may comprise a computer program product forperforming the operations presented herein. For example, such a computerprogram product may comprise a computer readable medium havinginstructions stored (and/or encoded) thereon, the instructions beingexecutable by one or more processors to perform the operations describedherein. For certain aspects, the computer program product may includepackaging material.

Software or instructions may also be transmitted over a transmissionmedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition oftransmission medium.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein can bedownloaded and/or otherwise obtained by a user terminal and/or basestation as applicable. For example, such a device can be coupled to aserver to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via storage means (e.g., RAM, ROM, a physical storage mediumsuch as a compact disc (CD) or floppy disk, etc.), such that a userterminal and/or base station can obtain the various methods uponcoupling or providing the storage means to the device. Moreover, anyother suitable technique for providing the methods and techniquesdescribed herein to a device can be utilized.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes and variations may be made in the arrangement, operation anddetails of the methods and apparatus described above without departingfrom the scope of the claims.

While the foregoing is directed to aspects of the present disclosure,other and further aspects of the disclosure may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

What is claimed is:
 1. A method of transmitting on a wirelesscommunication network, the method comprising: transmitting to one ormore first devices in a first portion of a bandwidth, the one or morefirst devices having a first set of capabilities; simultaneouslytransmitting to one or more second devices in a second portion of thebandwidth, the one or more second devices having a second set ofcapabilities; and wherein the transmission comprises a preamble whichincludes an indication for devices with the second set of capabilitiesto locate a frequency band in the bandwidth for symbols containing a setof transmission parameters for devices with the second set ofcapabilities, and where the indication is sent so as to have nosubstantial impact on a preamble decoding of devices with the first setof capabilities.
 2. The method of claim 1, wherein the indicationcomprises a code transmitted in the first portion of the bandwidth. 3.The method of claim 2, wherein the code is carried on an imaginary axisof data tones in one or more signal fields in the preamble.
 4. Themethod of claim 2, wherein the code comprises a one-bit code transmittedin the first portion of the bandwidth.
 5. The method of claim 1, whereinthe indication comprises a code transmitted in the second portion of thebandwidth.
 6. The method of claim 1, wherein the first portion of thebandwidth of the packet comprises a primary channel and the secondportion of the bandwidth comprises one or more secondary channels. 7.The method of claim 1, wherein the preamble is transmitted in the firstportion of the bandwidth, further comprising: transmitting one or morecopies of the preamble in each portion of the bandwidth that will beused to simultaneously transmit to the one or more second devices, atleast a portion of the one or more copies including the indication. 8.The method of claim 1, wherein simultaneously transmitting to one ormore second devices in a second portion of the bandwidth comprisessimultaneously transmitting a second preamble to one or more seconddevices in a second portion of the bandwidth, the second preambleincluding the set of transmission parameters for the one or more seconddevices having the second set of capabilities.
 9. The method of claim 8,wherein the transmission parameters include an indication of intendedrecipients of the transmission in the second portion of the bandwidth.10. An apparatus for wireless communication, comprising: a transmitterconfigured to transmit over a bandwidth, comprising: transmitting to oneor more first devices in a first portion of a bandwidth, the one or morefirst devices having a first set of capabilities; simultaneouslytransmitting to one or more second devices in a second portion of thebandwidth, the one or more second devices having a second set ofcapabilities; and wherein the transmission comprises a preamble whichincludes an indication for devices with the second set of capabilitiesto locate a frequency band in the bandwidth for symbols containing a setof transmission parameters for devices with the second set ofcapabilities, and where the indication is sent so as to have nosubstantial impact on a preamble decoding of devices with the first setof capabilities.
 11. The apparatus of claim 10, wherein the indicationcomprises a code transmitted in the first portion of the bandwidth. 12.The apparatus of claim 10, wherein the first portion of the bandwidth ofthe packet comprises a primary channel and wherein the second portion ofthe bandwidth of the packet comprises one or more secondary channels.13. The apparatus of claim 10, wherein the preamble is transmitted inthe first portion of the bandwidth, the transmitter further configuredto: transmit one or more copies of the preamble in each portion of thebandwidth that will be used to simultaneously transmit to the one ormore second devices, at least a portion of the one or more copiesincluding the indication.
 14. The apparatus of claim 10, whereinsimultaneously transmitting to one or more second devices in a secondportion of the bandwidth comprises simultaneously transmitting a secondpreamble to one or more second devices in a second portion of thebandwidth, the second preamble including the set of transmissionparameters for the one or more second devices having the second set ofcapabilities.
 15. A method of receiving on a wireless communicationnetwork, the method comprising: receiving a preamble in a first portionof a bandwidth, the preamble transmitted in a format compatible withdevices having a first set of capabilities; determining whether thepreamble contains information sufficient to inform devices having asecond set of capabilities to locate a signal field in a second portionof the bandwidth, wherein the first portion and the second portion ofthe bandwidth are non-overlapping; and receiving the signal field in thesecond portion of the bandwidth.
 16. The method of claim 15, furthercomprising receiving data in the second portion of the bandwidth. 17.The method of claim 15, wherein the first portion of the bandwidthcomprises a primary channel, and wherein the second portion of thebandwidth comprises one or more secondary channels.
 18. The method ofclaim 15, wherein the information comprises a one-bit code transmittedin the preamble.
 19. The method of claim 18, wherein the one-bit code iscarried on an imaginary axis of data tones in one or more signal fieldsin the preamble.
 20. The method of claim 15, wherein the information inthe preamble has no substantial impact on a preamble decoding of deviceswith the first set of capabilities.